diff --git a/Software/PC_Application/LibreVNA-GUI/Traces/trace.cpp b/Software/PC_Application/LibreVNA-GUI/Traces/trace.cpp
index 40b1761..74c4235 100644
--- a/Software/PC_Application/LibreVNA-GUI/Traces/trace.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/Traces/trace.cpp
@@ -427,6 +427,9 @@ QString Trace::getMathFormulaError() const
                     break;
                 }
             }
+            if(varName == "x") {
+                found = true;
+            }
             if(!found) {
                 return "Unknown variable: "+varName;
             }