Setting a Gabro bender

I've just dug my Gabro sheet metal bender out of 4 years of storage to bend up some missing panels from a machine and am having a mental blank
remembering how to set it up. I've down loaded the user instructions from the Gabro web site but they are vague on the point at issue.
I know that you need to set back the clamp bar from the fold bar by a certain number of metal gauge thicknesses - I've even found the various little 'L' shaped bits I bent years ago as gauges. The Gabro write up says 'turn until the correct gauges are pressed firmly into the corner formed by the bed and the fold bar' but nothing what so ever as to what thickness gauge one should use! Anyone using one of these bender can give me a clue?
AWEM
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Shear off a narrow strip of the sheet metal and experiment. It may not withstand a sharp bend without cracking.
jsw
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