Let me start by saying that I don't own a dedicated densitometer so my tests may not be classed as 100% but nevertheless, I shall proceed. Using a calibrated Stouffer 21 Transmission Step Wedge, I measured the density of each patch using the Densitometer in the VueScan Scanning Software and compared the results to what was written on the Stouffer sleeve. To my amazement, the values returned from Vuescan although not exactly the same, were very close indeed. Step 2 on the tablet is 0.20 and Vuescan reports 0.22 and this is true for all remaining steps. Armed with this information, I decided to expose a sheet of Fomapan 200 (4 stops) under what the spot meter exposure was. I rated this sheet at ISO 100 rather than the box speed of ISO 200. I pulled the dark slide 1/2 way out so that one half would be exposed at Zone 1 and the other half would be my Film Base + Fog I developed the sheet developed in Xtol for what I have been using as my normal development time (6 minutes @ 20°C) According to my sums, I should be getting a reading of the 0.26 on the exposed side of the negative which is 0.1 above Film Base + Fog. Readings obtained from Vuescan Densitometer The Film Base + Fog measures 0.16 The exposed side measures 0.22 To me, this indicates that ISO 100 would be a good value to use for this particular film.