diff --git a/matlab/TCV/gdat_tcv.m b/matlab/TCV/gdat_tcv.m
index 43a7b34b78067a271255050f71e197dc3ec2a5fa..17933ceefd2a2c134beca063da92dbee017036f6 100644
--- a/matlab/TCV/gdat_tcv.m
+++ b/matlab/TCV/gdat_tcv.m
@@ -2233,7 +2233,7 @@ elseif strcmp(mapping_for_tcv.method,'switchcase')
       gdat_data.units = 'particles/m^3';
       nel.dim{1} = neft.fit.t';
       nel.data = ones(size(nel.dim{1}));
-      gdat_data.r_center_chord = 0.903;
+      gdat_data.r_center_chord = 0.903; % mdsvalue('\diagz::fir_array:radii[5]') (6th chord is central)
       [ratio,fir_times,z_lineint]=fir_ratio_from_fits(neft.fit.data,neft.fit.x,psitbx01,nel,gdat_data.r_center_chord,gdat_data.t',1,1e3);
       gdat_data.data = reshape(1./ratio./z_lineint,numel(ratio),1);
       gdat_data.data_fullpath = ['line-averaged density from fit using ' neft.fit.data_fullpath];