diff --git a/CMakeLists.txt b/CMakeLists.txt
index 7f1d7b6a..8060fe0d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -388,30 +388,7 @@ find_package(Threads)
 
 find_package(Eigen3 REQUIRED)
 
-################################################################
-#
-# Locate CUDD bdd package.
-#
-find_library(CUDD_LIB
-  NAME cudd
-  PATHS ${CUDD_DIR}
-  PATH_SUFFIXES lib lib/cudd cudd/.libs
-  )
-if (CUDD_LIB)
-  message(STATUS "CUDD library: ${CUDD_LIB}")
-  get_filename_component(CUDD_LIB_DIR "${CUDD_LIB}" PATH)
-  get_filename_component(CUDD_LIB_PARENT1 "${CUDD_LIB_DIR}" PATH)
-  find_file(CUDD_HEADER cudd.h
-    PATHS ${CUDD_LIB_PARENT1} ${CUDD_LIB_PARENT1}/include ${CUDD_LIB_PARENT1}/include/cudd)
-  if (CUDD_HEADER)
-    get_filename_component(CUDD_INCLUDE "${CUDD_HEADER}" PATH)
-    message(STATUS "CUDD header: ${CUDD_HEADER}")
-  else()
-    message(STATUS "CUDD header: not found")
-  endif()
-else()
-  message(STATUS "CUDD library: not found")
-endif()
+include(cmake/FindCUDD.cmake)
 
 if("${SSTA}" STREQUAL "")
   set(SSTA 0)
@@ -479,7 +456,7 @@ set_source_files_properties(${STA_SWIG_CXX_FILE}
   PROPERTIES
   # No simple way to modify the swig template that emits code full of warnings
   # so suppress them.
-  COMPILE_OPTIONS "-Wno-cast-qual;-Wno-missing-braces;-Wno-deprecated-declarations"
+  COMPILE_OPTIONS "-Wunused-variable;-Wno-cast-qual;-Wno-missing-braces;-Wno-deprecated-declarations"
   )
 
 target_link_libraries(sta_swig
diff --git a/cmake/FindCUDD.cmake b/cmake/FindCUDD.cmake
new file mode 100644
index 00000000..170548d4
--- /dev/null
+++ b/cmake/FindCUDD.cmake
@@ -0,0 +1,25 @@
+################################################################
+#
+# Locate CUDD bdd package.
+#
+################################################################
+find_library(CUDD_LIB
+  NAME cudd
+  PATHS ${CUDD_DIR}
+  PATH_SUFFIXES lib lib/cudd cudd/.libs
+  )
+if (CUDD_LIB)
+  message(STATUS "CUDD library: ${CUDD_LIB}")
+  get_filename_component(CUDD_LIB_DIR "${CUDD_LIB}" PATH)
+  get_filename_component(CUDD_LIB_PARENT1 "${CUDD_LIB_DIR}" PATH)
+  find_file(CUDD_HEADER cudd.h
+    PATHS ${CUDD_LIB_PARENT1} ${CUDD_LIB_PARENT1}/include ${CUDD_LIB_PARENT1}/include/cudd)
+  if (CUDD_HEADER)
+    get_filename_component(CUDD_INCLUDE "${CUDD_HEADER}" PATH)
+    message(STATUS "CUDD header: ${CUDD_HEADER}")
+  else()
+    message(STATUS "CUDD header: not found")
+  endif()
+else()
+  message(STATUS "CUDD library: not found")
+endif()
diff --git a/doc/messages.txt b/doc/messages.txt
index 95adafbe..ea0fb51a 100644
--- a/doc/messages.txt
+++ b/doc/messages.txt
@@ -75,7 +75,6 @@
 0245 CheckTiming.cc:428        unknown print flag
 0246 Corner.cc:377             unknown parasitic analysis point count
 0247 Corner.cc:421             unknown analysis point count
-0248 Crpr.cc:73                missing prev paths
 0249 GatedClk.cc:247           illegal gated clock active value
 0250 NetworkEdit.tcl:107       unsupported object type $object_type.
 0252 NetworkEdit.tcl:174       unsupported object type $object_type.
@@ -422,72 +421,72 @@
 1240 LibertyReader.cc:3397     unknown port direction.
 1241 LibertyReader.cc:3644     max_transition is 0.0.
 1242 LibertyReader.cc:3750     pulse_latch unknown pulse type.
-1243 LibertyReader.cc:4194     timing group missing related_pin/related_bus_pin.
-1244 LibertyReader.cc:4293     unknown timing_type %s.
-1245 LibertyReader.cc:4313     unknown timing_sense %s.
-1246 LibertyReader.cc:4353     mode value is not a string.
-1247 LibertyReader.cc:4356     missing mode value.
-1248 LibertyReader.cc:4359     mode name is not a string.
-1249 LibertyReader.cc:4362     mode missing values.
-1250 LibertyReader.cc:4365     mode missing mode name and value.
-1251 LibertyReader.cc:4441     unsupported model axis.
-1252 LibertyReader.cc:4468     unsupported model axis.
-1253 LibertyReader.cc:4497     unsupported model axis.
-1254 LibertyReader.cc:4532     unsupported model axis.
-1255 LibertyReader.cc:4548     %s group not in timing group.
-1256 LibertyReader.cc:4587     table template %s not found.
-1257 LibertyReader.cc:4671     %s is missing values.
-1258 LibertyReader.cc:4694     %s is not a list of floats.
-1259 LibertyReader.cc:4696     table row has %u columns but axis has %d.
-1260 LibertyReader.cc:4706     table has %u rows but axis has %d.
-1261 LibertyReader.cc:4757     lut output is not a string.
-1262 LibertyReader.cc:4773     cell %s test_cell redefinition.
-1263 LibertyReader.cc:4821     mode definition missing name.
-1264 LibertyReader.cc:4838     mode value missing name.
-1265 LibertyReader.cc:4852     when attribute inside table model.
-1266 LibertyReader.cc:4901     %s attribute is not a string.
-1267 LibertyReader.cc:4904     %s is not a simple attribute.
-1268 LibertyReader.cc:4924     %s attribute is not an integer.
-1269 LibertyReader.cc:4927     %s is not a simple attribute.
-1270 LibertyReader.cc:4940     %s is not a simple attribute.
-1271 LibertyReader.cc:4966     %s value %s is not a float.
-1272 LibertyReader.cc:4995     %s missing values.
-1273 LibertyReader.cc:4999     %s missing values.
-1274 LibertyReader.cc:5002     %s is not a complex attribute.
-1275 LibertyReader.cc:5028     %s is not a float.
-1276 LibertyReader.cc:5051     %s is missing values.
-1277 LibertyReader.cc:5054     %s has more than one string.
-1278 LibertyReader.cc:5063     %s is missing values.
-1279 LibertyReader.cc:5088     %s attribute is not boolean.
-1280 LibertyReader.cc:5091     %s attribute is not boolean.
-1281 LibertyReader.cc:5094     %s is not a simple attribute.
-1282 LibertyReader.cc:5110     attribute %s value %s not recognized.
-1283 LibertyReader.cc:5141     unknown early/late value.
-1284 LibertyReader.cc:5361     OCV derate group named %s not found.
-1285 LibertyReader.cc:5377     ocv_derate missing name.
-1286 LibertyReader.cc:5430     unknown rise/fall.
-1287 LibertyReader.cc:5450     unknown derate type.
-1288 LibertyReader.cc:5482     unsupported model axis.
-1289 LibertyReader.cc:5514     unsupported model axis.
-1290 LibertyReader.cc:5546     unsupported model axis.
-1291 LibertyReader.cc:5617     unknown pg_type.
-1292 LibertyReader.cc:6031     port %s subscript out of range.
-1293 LibertyReader.cc:6035     port range %s of non-bus port %s.
-1294 LibertyReader.cc:6049     port %s not found.
-1295 LibertyReader.cc:6119     port %s not found.
+1243 LibertyReader.cc:4202     timing group missing related_pin/related_bus_pin.
+1244 LibertyReader.cc:4301     unknown timing_type %s.
+1245 LibertyReader.cc:4321     unknown timing_sense %s.
+1246 LibertyReader.cc:4361     mode value is not a string.
+1247 LibertyReader.cc:4364     missing mode value.
+1248 LibertyReader.cc:4367     mode name is not a string.
+1249 LibertyReader.cc:4370     mode missing values.
+1250 LibertyReader.cc:4373     mode missing mode name and value.
+1251 LibertyReader.cc:4449     unsupported model axis.
+1252 LibertyReader.cc:4476     unsupported model axis.
+1253 LibertyReader.cc:4505     unsupported model axis.
+1254 LibertyReader.cc:4540     unsupported model axis.
+1255 LibertyReader.cc:4556     %s group not in timing group.
+1256 LibertyReader.cc:4595     table template %s not found.
+1257 LibertyReader.cc:4679     %s is missing values.
+1258 LibertyReader.cc:4702     %s is not a list of floats.
+1259 LibertyReader.cc:4704     table row has %u columns but axis has %d.
+1260 LibertyReader.cc:4714     table has %u rows but axis has %d.
+1261 LibertyReader.cc:4765     lut output is not a string.
+1262 LibertyReader.cc:4781     cell %s test_cell redefinition.
+1263 LibertyReader.cc:4829     mode definition missing name.
+1264 LibertyReader.cc:4846     mode value missing name.
+1265 LibertyReader.cc:4860     when attribute inside table model.
+1266 LibertyReader.cc:4909     %s attribute is not a string.
+1267 LibertyReader.cc:4912     %s is not a simple attribute.
+1268 LibertyReader.cc:4932     %s attribute is not an integer.
+1269 LibertyReader.cc:4935     %s is not a simple attribute.
+1270 LibertyReader.cc:4948     %s is not a simple attribute.
+1271 LibertyReader.cc:4974     %s value %s is not a float.
+1272 LibertyReader.cc:5003     %s missing values.
+1273 LibertyReader.cc:5007     %s missing values.
+1274 LibertyReader.cc:5010     %s is not a complex attribute.
+1275 LibertyReader.cc:5036     %s is not a float.
+1276 LibertyReader.cc:5059     %s is missing values.
+1277 LibertyReader.cc:5062     %s has more than one string.
+1278 LibertyReader.cc:5071     %s is missing values.
+1279 LibertyReader.cc:5096     %s attribute is not boolean.
+1280 LibertyReader.cc:5099     %s attribute is not boolean.
+1281 LibertyReader.cc:5102     %s is not a simple attribute.
+1282 LibertyReader.cc:5118     attribute %s value %s not recognized.
+1283 LibertyReader.cc:5149     unknown early/late value.
+1284 LibertyReader.cc:5369     OCV derate group named %s not found.
+1285 LibertyReader.cc:5385     ocv_derate missing name.
+1286 LibertyReader.cc:5438     unknown rise/fall.
+1287 LibertyReader.cc:5458     unknown derate type.
+1288 LibertyReader.cc:5490     unsupported model axis.
+1289 LibertyReader.cc:5522     unsupported model axis.
+1290 LibertyReader.cc:5554     unsupported model axis.
+1291 LibertyReader.cc:5625     unknown pg_type.
+1292 LibertyReader.cc:6039     port %s subscript out of range.
+1293 LibertyReader.cc:6043     port range %s of non-bus port %s.
+1294 LibertyReader.cc:6057     port %s not found.
+1295 LibertyReader.cc:6127     port %s not found.
 1297 LibertyReader.cc:1466     axis type %s not supported.
 1298 LibertyReader.cc:2180     statetable input port %s not found.
 1299 LibertyReader.cc:3809     unknown signal_type %s.
-1300 LibertyReader.cc:4068     table row must have 3 groups separated by ':'.
-1301 LibertyReader.cc:4073     table row has %zu input values but %zu are required.
-1302 LibertyReader.cc:4080     table row has %zu current values but %zu are required.
-1303 LibertyReader.cc:4087     table row has %zu next values but %zu are required.
-1304 LibertyReader.cc:4133     table input value '%s' not recognized.
-1305 LibertyReader.cc:4152     table internal value '%s' not recognized.
-1340 LibertyWriter.cc:307      %s/%s bundled ports not supported.
-1341 LibertyWriter.cc:455      %s/%s/%s timing model not supported.
-1342 LibertyWriter.cc:475      3 axis table models not supported.
-1343 LibertyWriter.cc:624      %s/%s/%s timing arc type %s not supported.
+1300 LibertyReader.cc:4076     table row must have 3 groups separated by ':'.
+1301 LibertyReader.cc:4081     table row has %zu input values but %zu are required.
+1302 LibertyReader.cc:4088     table row has %zu current values but %zu are required.
+1303 LibertyReader.cc:4095     table row has %zu next values but %zu are required.
+1304 LibertyReader.cc:4141     table input value '%s' not recognized.
+1305 LibertyReader.cc:4160     table internal value '%s' not recognized.
+1340 LibertyWriter.cc:308      %s/%s bundled ports not supported.
+1341 LibertyWriter.cc:456      %s/%s/%s timing model not supported.
+1342 LibertyWriter.cc:476      3 axis table models not supported.
+1343 LibertyWriter.cc:625      %s/%s/%s timing arc type %s not supported.
 1350 LumpedCapDelayCalc.cc:138 gate delay input variable is NaN
 1355 MakeTimingModel.cc:227    clock %s pin %s is inside model block.
 1360 Vcd.cc:172                Unknown variable %s ID %s
@@ -505,17 +504,15 @@
 1525 SpefParse.yy:805          %d is not positive.
 1526 SpefParse.yy:814          %.4f is not positive.
 1527 SpefParse.yy:820          %.4f is not positive.
-1550 Sta.cc:1999               '%s' is not a valid start point.
-1551 Sta.cc:2072               '%s' is not a valid endpoint.
-1552 Sta.cc:2075               '%s' is not a valid endpoint.
-1553 Sta.cc:2391               maximum corner count exceeded
-1554 Sta.cc:1996               '%s' is not a valid start point.
-1570 Search.i:54               no network has been linked.
-1571 Search.i:68               network does not support edits.
-1574 Search.i:1121             POCV support requires compilation with SSTA=1.
-1575 Search.i:530              unknown report path field %s
-1576 Search.i:542              unknown report path field %s
-1600 WritePathSpice.cc:165     No liberty libraries found,
+1550 Sta.cc:2000               '%s' is not a valid start point.
+1551 Sta.cc:2073               '%s' is not a valid endpoint.
+1552 Sta.cc:2076               '%s' is not a valid endpoint.
+1553 Sta.cc:2393               maximum corner count exceeded
+1554 Sta.cc:1997               '%s' is not a valid start point.
+1570 Sta.cc:3413               No network has been linked.
+1574 Search.i:1026             POCV support requires compilation with SSTA=1.
+1575 Search.i:465              unknown report path field %s
+1576 Search.i:477              unknown report path field %s
 1602 WriteSpice.cc:458         Liberty pg_port %s/%s missing voltage_name attribute,
 1603 WriteSpice.cc:428         %s pg_port %s not found,
 1604 WriteSpice.cc:1019        no register/latch found for path from %s to %s,
@@ -575,7 +572,10 @@
 2103 ArcDelayCalc.cc:97        %s not a valid rise/fall.
 2104 ArcDelayCalc.cc:100       Pin %s/%s not found.
 2105 ArcDelayCalc.cc:103       Instance %s not found.
-2120 Network.i:252             unknown namespace
-2121 Sdc.i:105                 unknown analysis type
-2122 Sdc.i:232                 unknown wire load mode
-2140 StaTclTypes.i:431         Delay calc arg requires 5 or 6 args.
+2120 Network.i:255             unknown namespace
+2121 Sdc.i:104                 unknown analysis type
+2122 Sdc.i:227                 unknown wire load mode
+2140 StaTclTypes.i:424         Delay calc arg requires 5 or 6 args.
+2141 Sta.cc:3417               No liberty libraries found.
+2200 Crpr.cc:62                missing prev paths
+2201 Crpr.cc:73                missing prev paths
diff --git a/graph/DelayNormal1.cc b/graph/DelayNormal1.cc
index 294766c1..603c012d 100644
--- a/graph/DelayNormal1.cc
+++ b/graph/DelayNormal1.cc
@@ -63,6 +63,12 @@ Delay::Delay(const Delay &delay) :
 {
 }
 
+Delay::Delay(const DelayDbl &delay) :
+  mean_(delay.mean_),
+  sigma2_(delay.sigma2_)
+{
+}
+
 Delay::Delay(float mean) :
   mean_(mean),
   sigma2_(0.0)
@@ -173,6 +179,35 @@ Delay::operator==(const Delay &delay) const
 
 ////////////////////////////////////////////////////////////////
 
+DelayDbl::DelayDbl() :
+  mean_(0.0),
+  sigma2_(0.0)
+{
+}
+
+void
+DelayDbl::operator=(float delay)
+{
+  mean_ = delay;
+  sigma2_ = 0.0;
+}
+
+void
+DelayDbl::operator+=(const Delay &delay)
+{
+  mean_ += delay.mean_;
+  sigma2_ += delay.sigma2_;
+}
+
+void
+DelayDbl::operator-=(const Delay &delay)
+{
+  mean_ -= delay.mean_;
+  sigma2_ += delay.sigma2_;
+}
+
+////////////////////////////////////////////////////////////////
+
 Delay
 makeDelay(float delay,
 	  float sigma,
diff --git a/graph/DelayNormal2.cc b/graph/DelayNormal2.cc
index 4bdd482b..bd444e51 100644
--- a/graph/DelayNormal2.cc
+++ b/graph/DelayNormal2.cc
@@ -64,6 +64,13 @@ Delay::Delay(const Delay &delay) :
   sigma2_[EarlyLate::lateIndex()] = delay.sigma2_[EarlyLate::lateIndex()];
 }
 
+Delay::Delay(const DelayDbl &delay) :
+  mean_(delay.mean_)
+{
+  sigma2_[EarlyLate::earlyIndex()] = delay.sigma2_[EarlyLate::earlyIndex()];
+  sigma2_[EarlyLate::lateIndex()] = delay.sigma2_[EarlyLate::lateIndex()];
+}
+
 Delay::Delay(float mean) :
   mean_(mean),
   sigma2_{0.0, 0.0}
@@ -196,6 +203,38 @@ Delay::operator==(const Delay &delay) const
 
 ////////////////////////////////////////////////////////////////
 
+DelayDbl::DelayDbl() :
+  mean_(0.0),
+  sigma2_{0.0, 0.0}
+{
+}
+
+void
+DelayDbl::operator=(float delay)
+{
+  mean_ = delay;
+  sigma2_[early_index] = 0.0;
+  sigma2_[late_index] = 0.0;
+}
+
+void
+DelayDbl::operator+=(const Delay &delay)
+{
+  mean_ += delay.mean_;
+  sigma2_[early_index] += delay.sigma2_[early_index];
+  sigma2_[late_index] += delay.sigma2_[late_index];
+}
+
+void
+DelayDbl::operator-=(const Delay &delay)
+{
+  mean_ -= delay.mean_;
+  sigma2_[early_index] += delay.sigma2_[early_index];
+  sigma2_[late_index] += delay.sigma2_[late_index];
+}
+
+////////////////////////////////////////////////////////////////
+
 Delay
 makeDelay(float delay,
 	  float sigma_early,
diff --git a/include/sta/DelayFloat.hh b/include/sta/DelayFloat.hh
index 68143025..800c7e03 100644
--- a/include/sta/DelayFloat.hh
+++ b/include/sta/DelayFloat.hh
@@ -25,6 +25,8 @@ namespace sta {
 class StaState;
 
 typedef float Delay;
+// Delay double for accumulating Delays.
+typedef double DelayDbl;
 
 const Delay delay_zero = 0.0;
 
diff --git a/include/sta/DelayNormal1.hh b/include/sta/DelayNormal1.hh
index a8bbacc8..103fe881 100644
--- a/include/sta/DelayNormal1.hh
+++ b/include/sta/DelayNormal1.hh
@@ -21,6 +21,7 @@
 namespace sta {
 
 class Delay;
+class DelayDbl;
 class StaState;
 
 // Normal distribution with std deviation.
@@ -29,6 +30,7 @@ class Delay
 public:
   Delay();
   Delay(const Delay &delay);
+  Delay(const DelayDbl &delay);
   Delay(float mean);
   Delay(float mean,
 	float sigma2);
@@ -53,6 +55,29 @@ private:
   float mean_;
   // Sigma^2
   float sigma2_;
+
+  friend class DelayDbl;
+};
+
+// Dwlay with doubles for accumulating delays.
+class DelayDbl
+{
+public:
+  DelayDbl();
+  float mean() const { return mean_; }
+  float sigma() const;
+  // sigma^2
+  float sigma2() const;
+  void operator=(float delay);
+  void operator+=(const Delay &delay);
+  void operator-=(const Delay &delay);
+
+private:
+  double mean_;
+  // Sigma^2
+  double sigma2_;
+
+  friend class Delay;
 };
 
 const Delay delay_zero(0.0);
diff --git a/include/sta/DelayNormal2.hh b/include/sta/DelayNormal2.hh
index f7aac325..5f77eacd 100644
--- a/include/sta/DelayNormal2.hh
+++ b/include/sta/DelayNormal2.hh
@@ -21,6 +21,7 @@
 namespace sta {
 
 class Delay;
+class DelayDbl;
 class StaState;
 
 // Normal distribution with early(left)/late(right) std deviations.
@@ -29,6 +30,7 @@ class Delay
 public:
   Delay();
   Delay(const Delay &delay);
+  Delay(const DelayDbl &delay);
   Delay(float mean);
   Delay(float mean,
 	float sigma2_early,
@@ -60,6 +62,33 @@ private:
   float mean_;
   // Sigma^2
   float sigma2_[EarlyLate::index_count];
+
+  friend class DelayDbl;
+};
+
+// Dwlay with doubles for accumulating delays.
+class DelayDbl
+{
+public:
+  DelayDbl();
+  float mean() const { return mean_; }
+  float sigma() const;
+  // sigma^2
+  float sigma2() const;
+  void operator=(float delay);
+  void operator+=(const Delay &delay);
+  void operator-=(const Delay &delay);
+
+protected:
+  static const int early_index = 0;
+  static const int late_index = 1;
+
+private:
+  double mean_;
+  // Sigma^2
+  double sigma2_[EarlyLate::index_count];
+
+  friend class Delay;
 };
 
 const Delay delay_zero(0.0);
diff --git a/include/sta/Search.hh b/include/sta/Search.hh
index 5b3d6772..8dce6775 100644
--- a/include/sta/Search.hh
+++ b/include/sta/Search.hh
@@ -60,6 +60,7 @@ typedef UnorderedSet<TagGroup*, TagGroupHash, TagGroupEqual> TagGroupSet;
 typedef Map<Vertex*, Slack> VertexSlackMap;
 typedef Vector<VertexSlackMap> VertexSlackMapSeq;
 typedef Vector<WorstSlacks> WorstSlacksSeq;
+typedef vector<DelayDbl> DelayDblSeq;
 
 class Search : public StaState
 {
@@ -570,7 +571,7 @@ protected:
   // Endpoint vertices with slacks that have changed since tns was found.
   VertexSet *invalid_tns_;
   // Indexed by path_ap->index().
-  SlackSeq tns_;
+  DelayDblSeq tns_;
   // Indexed by path_ap->index().
   VertexSlackMapSeq tns_slacks_;
   std::mutex tns_lock_;
diff --git a/parasitics/SpefReader.cc b/parasitics/SpefReader.cc
index 2eba572e..7b331f99 100644
--- a/parasitics/SpefReader.cc
+++ b/parasitics/SpefReader.cc
@@ -168,7 +168,12 @@ SpefReader::findInstanceRelative(const char *name)
 Net *
 SpefReader::findNetRelative(const char *name)
 {
-  return network_->findNetRelative(instance_, name);
+  Net *net = network_->findNetRelative(instance_, name);
+  // Relax spef escaping requirement because some commercial tools
+  // don't follow the rules.
+  if (net == nullptr)
+    net = sdc_network_->findNetRelative(instance_, name);
+  return net;
 }
 
 Pin *
diff --git a/search/MakeTimingModel.cc b/search/MakeTimingModel.cc
index e994461f..8ac52a7f 100644
--- a/search/MakeTimingModel.cc
+++ b/search/MakeTimingModel.cc
@@ -98,7 +98,6 @@ MakeTimingModel::makeTimingModel()
   makePorts();
 
   sta_->searchPreamble();
-  graph_ = sta_->graph();
 
   findTimingFromInputs();
   findClkedOutputPaths();
@@ -143,12 +142,7 @@ MakeTimingModel::makeLibrary()
 {
   library_ = network_->makeLibertyLibrary(lib_name_, filename_);
   LibertyLibrary *default_lib = network_->defaultLibertyLibrary();
-  *library_->units()->timeUnit() = *default_lib->units()->timeUnit();
-  *library_->units()->capacitanceUnit() = *default_lib->units()->capacitanceUnit();
-  *library_->units()->voltageUnit() = *default_lib->units()->voltageUnit();
-  *library_->units()->resistanceUnit() = *default_lib->units()->resistanceUnit();
-  *library_->units()->powerUnit() = *default_lib->units()->powerUnit();
-  *library_->units()->distanceUnit() = *default_lib->units()->distanceUnit();
+  *library_->units() = *default_lib->units();
 
   for (RiseFall *rf : RiseFall::range()) {
     library_->setInputThreshold(rf, default_lib->inputThreshold(rf));
diff --git a/search/Sta.cc b/search/Sta.cc
index 09287127..d26b6f1c 100644
--- a/search/Sta.cc
+++ b/search/Sta.cc
@@ -5651,6 +5651,7 @@ Sta::writeTimingModel(const char *lib_name,
                       const bool scalar)
 {
   ensureLinked();
+  ensureGraph();
   LibertyLibrary *library = makeTimingModel(lib_name, cell_name, filename,
                                             corner, scalar, this);
   writeLiberty(library, filename, this);
diff --git a/search/WorstSlack.cc b/search/WorstSlack.cc
index a6dae0d5..2aacdc49 100644
--- a/search/WorstSlack.cc
+++ b/search/WorstSlack.cc
@@ -265,32 +265,34 @@ WorstSlack::updateWorstSlack(Vertex *vertex,
 			     SlackSeq &slacks,
 			     PathAPIndex path_ap_index)
 {
-  Slack slack = slacks[path_ap_index];
-
-  // Locking is required because ArrivalVisitor is called by multiple
-  // threads.
-  LockGuard lock(lock_);
-  if (worst_vertex_
-      && delayLess(slack, worst_slack_, this))
-    setWorstSlack(vertex, slack);
-  else if (vertex == worst_vertex_)
-    // Mark worst slack as unknown (updated by findWorstSlack().
-    worst_vertex_ = nullptr;
-
-  if (!delayEqual(slack, slack_init_)
-      && delayLessEqual(slack, slack_threshold_, this)) {
-    debugPrint(debug_, "wns", 3, "insert %s %s",
-               vertex->name(network_),
-               delayAsString(slack, this));
-    queue_->insert(vertex);
-  }
-  else {
-    debugPrint(debug_, "wns", 3, "delete %s %s",
-               vertex->name(network_),
-               delayAsString(slack, this));
-    queue_->erase(vertex);
+  // Do not touch the state unless queue has been initialized
+  if (!queue_->empty()) {
+    Slack slack = slacks[path_ap_index];
+    // Locking is required because ArrivalVisitor is called by multiple
+    // threads.
+    LockGuard lock(lock_);
+    if (worst_vertex_
+        && delayLess(slack, worst_slack_, this))
+      setWorstSlack(vertex, slack);
+    else if (vertex == worst_vertex_)
+      // Mark worst slack as unknown (updated by findWorstSlack().
+      worst_vertex_ = nullptr;
+
+    if (!delayEqual(slack, slack_init_)
+        && delayLessEqual(slack, slack_threshold_, this)) {
+      debugPrint(debug_, "wns", 3, "insert %s %s",
+                 vertex->name(network_),
+                 delayAsString(slack, this));
+      queue_->insert(vertex);
+    }
+    else {
+      debugPrint(debug_, "wns", 3, "delete %s %s",
+                 vertex->name(network_),
+                 delayAsString(slack, this));
+      queue_->erase(vertex);
+    }
+    //checkQueue(path_ap_index);
   }
-  //  checkQueue();
 }
 
 void