With my recent order of supplies I purchased some Ilford MGIV FB paper and I finally got around to determining the relative ISO Range Numbers through the process described in Anchell's Variable Contrast Printing Manual. I thought I would share the results. The range numbers were determined while using the combination: LPL 4550 XLG VCCE (diffused quartz-halogen light source). A Stouffer 21-step tablet was projected onto an 8x10 sheet for each filter setting; the sheets were then developed in Dektol (1:3) for 3 minutes, results not read until toned in selenium (1:10), sheets dried in a microwave. I used 9 sheets, 2 for nailing the proper exposure time. The attacment shows a contrast equivalent chart that I scanned from the text, with each of my filtration settings shown in "red", then inserted in the chart in line with the RN result for that filter and the associated contrast grade numbers; a sheet was also used for a "No Filter" exposure. Besides knowing what RN is produced with each of my filtration settings, the other most important information is the spacing between each filter. Sometimes two adjacent filtration settings can produce identical RNs, therefore it would be a waste of time and paper switching to the next setting if it did not increase the desired contrast.