diff --git a/src/draw.c b/src/draw.c
index bfc78d86..f89a4f11 100644
--- a/src/draw.c
+++ b/src/draw.c
@@ -3147,7 +3147,7 @@ int calc_custom_data_yrange(int sweep_idx, const char *express, Graph_ctx *gr)
         if(xx > end || xx < start ||         /* ... and we ran out of graph area ... */
           wrap) {                          /* ... or sweep variable changed direction */
           if(dataset == -1 || dataset == sweepvar_wrap) {
-            idx = plot_raw_custom_data(sweep_idx, first, last, express);
+            idx = plot_raw_custom_data(sweep_idx, first, last, express, NULL);
           }
           first = -1;
         }
@@ -3164,7 +3164,7 @@ int calc_custom_data_yrange(int sweep_idx, const char *express, Graph_ctx *gr)
     } /* for(p = ofs ; p < ofs + raw->npoints[dset]; p++) */
     if(first != -1) {
       if(dataset == -1 || dataset == sweepvar_wrap) {
-        idx = plot_raw_custom_data(sweep_idx, first, last, express);
+        idx = plot_raw_custom_data(sweep_idx, first, last, express, NULL);
       }
     }
     /* offset pointing to next dataset */
@@ -3258,7 +3258,7 @@ int find_closest_wave(int i, Graph_ctx *gr)
         register SPICE_DATA *gvx = raw->values[sweep_idx];
         register SPICE_DATA *gvy;
         ofs_end = ofs + raw->npoints[dset];
-        if(expression) plot_raw_custom_data(sweep_idx, ofs, ofs_end - 1, express);
+        if(expression) plot_raw_custom_data(sweep_idx, ofs, ofs_end - 1, express, NULL);
         gvy = raw->values[idx];
         dbg(1, "find_closest_wave(): dset=%d\n", dset);
         first = -1;
@@ -3551,7 +3551,7 @@ void draw_graph(int i, const int flags, Graph_ctx *gr, void *ct)
                                    sweep_idx, wcnt, n_nodes, gr, ct);
                     }
                   } else {
-                    if(expression) idx = plot_raw_custom_data(sweep_idx, first, last, express);
+                    if(expression) idx = plot_raw_custom_data(sweep_idx, first, last, express, NULL);
                     draw_graph_points(idx, first, last, point, wave_color, wcnt, n_nodes, gr, ct);
                   }
                 }
@@ -3594,7 +3594,7 @@ void draw_graph(int i, const int flags, Graph_ctx *gr, void *ct)
                                sweep_idx, wcnt, n_nodes, gr, ct);
                 }
               } else {
-                if(expression) idx = plot_raw_custom_data(sweep_idx, first, last, express);
+                if(expression) idx = plot_raw_custom_data(sweep_idx, first, last, express, NULL);
                 draw_graph_points(idx, first, last, point, wave_color, wcnt, n_nodes, gr, ct);
               }
             }
diff --git a/src/save.c b/src/save.c
index 1af1db32..ded369ec 100644
--- a/src/save.c
+++ b/src/save.c
@@ -824,30 +824,34 @@ int raw_read_from_attr(Raw **rawptr, const char *type, double sweep1, double swe
   return res;
 }
 
-int raw_add_vector(const char *varname)
+int raw_add_vector(const char *varname, const char *expr)
 {
   int f;
+  int res = 0;
   Raw *raw = xctx->raw;
   if(!raw || !raw->values) return 0;
 
-  if(int_hash_lookup(&raw->table, varname, 0, XLOOKUP)) {
-    return 0;
+  if(!int_hash_lookup(&raw->table, varname, 0, XLOOKUP)) {
+    raw->nvars++;
+    my_realloc(_ALLOC_ID_, &raw->names, raw->nvars * sizeof(char *));
+    my_realloc(_ALLOC_ID_, &raw->cursor_b_val, raw->nvars * sizeof(double));
+    raw->cursor_b_val[raw->nvars - 1] = 0.0;
+    raw->names[raw->nvars - 1] = NULL;
+    my_strdup2(_ALLOC_ID_, &raw->names[raw->nvars - 1], varname);
+    int_hash_lookup(&raw->table, raw->names[raw->nvars - 1], raw->nvars - 1, XINSERT_NOREPLACE);
+    my_realloc(_ALLOC_ID_, &raw->values, (raw->nvars + 1) * sizeof(SPICE_DATA *));
+    raw->values[raw->nvars] = NULL;
+    my_realloc(_ALLOC_ID_, &raw->values[raw->nvars], raw->allpoints * sizeof(SPICE_DATA));
+    res = 1;
   }
-  raw->nvars++;
-  my_realloc(_ALLOC_ID_, &raw->names, raw->nvars * sizeof(char *));
-  my_realloc(_ALLOC_ID_, &raw->cursor_b_val, raw->nvars * sizeof(double));
-  raw->cursor_b_val[raw->nvars - 1] = 0.0;
-  raw->names[raw->nvars - 1] = NULL;
-  my_strdup2(_ALLOC_ID_, &raw->names[raw->nvars - 1], varname);
-  int_hash_lookup(&raw->table, raw->names[raw->nvars - 1], raw->nvars - 1, XINSERT_NOREPLACE);
-
-  my_realloc(_ALLOC_ID_, &raw->values, (raw->nvars + 1) * sizeof(SPICE_DATA *));
-  raw->values[raw->nvars] = NULL;
-  my_realloc(_ALLOC_ID_, &raw->values[raw->nvars], raw->allpoints * sizeof(SPICE_DATA));
-  for(f = 0; f < raw->allpoints; f++) {
-    raw->values[raw->nvars - 1][f] = 0.0;
+  if(expr) {
+    plot_raw_custom_data(0, 0, raw->allpoints, expr, varname);
+  } else if(res == 1) {
+    for(f = 0; f < raw->allpoints; f++) {
+      raw->values[raw->nvars - 1][f] = 0.0;
+    }
   }
-  return 1;
+  return res;
 }
 
 /* read a ngspice raw file (with data portion in binary format) */
@@ -1459,7 +1463,7 @@ typedef struct {
   int prevp;
 } Stack1;
 
-int plot_raw_custom_data(int sweep_idx, int first, int last, const char *expr)
+int plot_raw_custom_data(int sweep_idx, int first, int last, const char *expr, const char *yname)
 {
   int i, p, idx;
   const char *n;
@@ -1467,10 +1471,17 @@ int plot_raw_custom_data(int sweep_idx, int first, int last, const char *expr)
   Stack1 stack1[STACKMAX];
   double stack2[STACKMAX]={0}, tmp, result, avg;
   int stackptr1 = 0, stackptr2 = 0;
-  SPICE_DATA *y = xctx->raw->values[xctx->raw->nvars]; /* custom plot data column */
+  SPICE_DATA *y;
   SPICE_DATA *x = xctx->raw->values[sweep_idx];
   SPICE_DATA *sweepx = xctx->raw->values[0];
 
+  y = xctx->raw->values[xctx->raw->nvars]; /* custom plot data column */
+  if(yname != NULL) {
+    int yidx = get_raw_index(yname);
+    if(yidx >= 0) {
+      y = xctx->raw->values[yidx]; /* provided index */
+    }
+  }
   my_strdup2(_ALLOC_ID_, &ntok_copy, expr);
   ntok_ptr = ntok_copy;
   dbg(1, "plot_raw_custom_data(): expr=%s\n", expr);
diff --git a/src/scheduler.c b/src/scheduler.c
index 8b3feb86..85fb2faf 100644
--- a/src/scheduler.c
+++ b/src/scheduler.c
@@ -3502,7 +3502,11 @@ int xschem(ClientData clientdata, Tcl_Interp *interp, int argc, const char * arg
      *     xschem raw_query points [dset]: print simulation points for
      *     dataset 'dset' (default: all dataset points combined)
      *   xschem raw_query set node n value [dataset]: change loaded raw file data node[n] to value
-     *   xschem raw_query add varname: add a 'varname' vector with all values set to 0 to loaded raw file
+     *   xschem raw_query add varname [expr]
+     *     add a 'varname' vector with all values set to 0 to loaded raw file if expr not given
+     *     otherwise initialize data with values calculated from expr.
+     *     If varname is already existing and expr given recalculate data
+     *     Example: xschem raw_query add power {outm outp - i(@r1[i]) *}
      *     
      */
     else if(!strcmp(argv[1], "raw_query"))
@@ -3560,7 +3564,11 @@ int xschem(ClientData clientdata, Tcl_Interp *interp, int argc, const char * arg
           }
         } else if(argc > 3 && !strcmp(argv[2], "add")) {
           int res = 0;
-          res = raw_add_vector(argv[3]);
+          if(argc > 4) {
+            res = raw_add_vector(argv[3], argv[4]);
+          } else {
+            res = raw_add_vector(argv[3], NULL);
+          }
           Tcl_SetResult(interp, my_itoa(res), TCL_VOLATILE); 
         } else if(argc > 2 && !strcmp(argv[2], "datasets")) {
           Tcl_SetResult(interp, my_itoa(raw->datasets), TCL_VOLATILE); 
diff --git a/src/xschem.h b/src/xschem.h
index c43eca14..75523d62 100644
--- a/src/xschem.h
+++ b/src/xschem.h
@@ -1223,7 +1223,7 @@ extern int filter_data(const char *din, const size_t ilen,
 extern int embed_rawfile(const char *rawfile);
 extern int read_rawfile_from_attr(const char *b64s, size_t length, const char *type);
 extern int raw_read_from_attr(Raw **rawptr, const char *type, double sweep1, double sweep2);
-extern int raw_add_vector(const char *varname);
+extern int raw_add_vector(const char *varname, const char *expr);
 extern int new_rawfile(const char *name, const char *type, const char *sweepvar,
                        double start, double step, int number);
 extern char *base64_from_file(const char *f, size_t *length);
@@ -1244,7 +1244,7 @@ extern int extra_rawfile(int what, const char *f, const char *type, double sweep
 extern int raw_read(const char *f, Raw **rawptr, const char *type, double sweep1, double sweep2);
 extern int table_read(const char *f);
 extern double get_raw_value(int dataset, int idx, int point);
-extern int plot_raw_custom_data(int sweep_idx, int first, int last, const char *ntok);
+extern int plot_raw_custom_data(int sweep_idx, int first, int last, const char *ntok, const char *yname);
 extern int calc_custom_data_yrange(int sweep_idx, const char *express, Graph_ctx *gr);
 extern int sch_waves_loaded(void);
 extern int edit_wave_attributes(int what, int i, Graph_ctx *gr);