diff --git a/V4/demo/demo.exe b/V4/demo/demo.exe
index 202dcd4..0da209a 100644
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diff --git a/V4/demo/demo.ilk b/V4/demo/demo.ilk
index 8834840..0e4e4f1 100644
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diff --git a/V4/demo/demo.obj b/V4/demo/demo.obj
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diff --git a/V4/demo/demo.pdb b/V4/demo/demo.pdb
index 88c2387..760fc56 100644
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diff --git a/V4/demo/vc140.pdb b/V4/demo/vc140.pdb
index ab79e48..502ca24 100644
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diff --git a/V4/econSpd.h b/V4/econSpd.h
index 0fac4e1..90114ad 100644
--- a/V4/econSpd.h
+++ b/V4/econSpd.h
@@ -94,7 +94,7 @@ float interp(float lower, float upper, float ratio) {
 /// @param weight Weight in kilogrammes
 /// @param tipTankPercent Lowest tip tank quantity (left/right) in percent
 /// @param ci CI
-/// @return Mach corresponding to CI
+/// @return Mach corresponding to CI. Returns -1 if not possible
 float ci2mach(float altitude, float weight, float tipTankPercent, int ci) {
   auto [lowerFl, upperFl, ratioFl] = boundAltitude(altitude);
   auto [lowerWgt, upperWgt, ratioWgt] = boundWeight(weight);