diff --git a/LuaLibs/CalcPaths.lua b/LuaLibs/CalcPaths.lua
index 4268837..70dc021 100644
--- a/LuaLibs/CalcPaths.lua
+++ b/LuaLibs/CalcPaths.lua
@@ -955,7 +955,7 @@ end
 --------------------------------------------------------------------
 local function UpdateTotalShellSurf( nSrf, nCrv, dStrand, nGrpId)
 
-   local nSrfExtraShell = EgtSurfFrFatCurve( nGrpId, nCrv, dStrand + s_dOffsCorr, false)
+   local nSrfExtraShell = EgtSurfFrFatCurve( nGrpId, nCrv, dStrand - s_dOffsCorr, false)
    if nSrfExtraShell then
       local vtSrfN = EgtSurfFrNormVersor( nSrf, GDB_ID.ROOT)
       local vtSrfExShN = EgtSurfFrNormVersor( nSrfExtraShell, GDB_ID.ROOT)