diff --git a/doc/xschem_man/developer_info.html b/doc/xschem_man/developer_info.html
index 2d795720..0cc1b8b6 100644
--- a/doc/xschem_man/developer_info.html
+++ b/doc/xschem_man/developer_info.html
@@ -760,6 +760,7 @@ C {verilog_timescale.sym} 1050 -100 0 0 {name=s1 timestep="1ns" precision="1ns"
      <li><kbd> bbox </kbd> bounding box schematic </li>
      <li><kbd> bbox_hilighted </kbd> bounding box of highlinhted objects </li>
      <li><kbd> bbox_selected </kbd> bounding box of selected objects </li>
+     <li><kbd> build_date </kbd> time and date this file was built. </li>
      <li><kbd> cadlayers </kbd> number of layers </li>
      <li><kbd> case_insensitive </kbd> case_insensitive symbol matching </li>
      <li><kbd> color_ps </kbd> color postscript flag </li>
diff --git a/src/scheduler.c b/src/scheduler.c
index 21292799..38e6866e 100644
--- a/src/scheduler.c
+++ b/src/scheduler.c
@@ -1344,6 +1344,10 @@ int xschem(ClientData clientdata, Tcl_Interp *interp, int argc, const char * arg
             my_snprintf(res, S(res), "%g %g %g %g", boundbox.x1, boundbox.y1, boundbox.x2, boundbox.y2);
             Tcl_SetResult(interp, res, TCL_VOLATILE);
           }
+          else if(!strcmp(argv[2], "build_date")) { /* time and date this file was built. */
+            char date[] =  __DATE__ " : "  __TIME__;
+            Tcl_SetResult(interp, date,  TCL_STATIC);
+          }
           break;
           case 'c':
           if(!strcmp(argv[2], "cadlayers")) { /* number of layers */
diff --git a/src/xschem.tcl b/src/xschem.tcl
index 56fcda69..a3ed1fd3 100644
--- a/src/xschem.tcl
+++ b/src/xschem.tcl
@@ -731,6 +731,17 @@ proc cdiv {a b} {
   return $c
 }
 
+# 1/b
+proc cinv {b} {
+
+  lassign $b rb ib
+  set rb [expr {double($rb)}]
+  set ib [expr {double($ib)}]
+  set m [expr {$rb * $rb + $ib * $ib}]
+  set c [list [expr {$rb / $m}] [expr {-$ib / $m}]]
+  return $c
+}
+
 # return real component
 proc creal {a} {
   lassign $a ra ia