--- a/svghmi/widgets_common.ysl2	Mon Aug 03 16:32:23 2020 +0200
+++ b/svghmi/widgets_common.ysl2	Mon Aug 03 16:34:44 2020 +0200
@@ -105,6 +105,10 @@
             }
         }
 
+        get_idx(index) {
+             let orig = this.indexes[index];
+             return this.offset ? orig + this.offset : orig;
+        }
     }
     ||
 }