Expert needed - Sinar extension gauge

Here is a link for a Sinar extension gauge and pencil. I have one just like it but do not have any instructions. Should be easy to figure out how to use this tool, but I can't. Anyone know how to use this thing? Is it held up to the bellows before and after focusing somehow? Anyone have instructions they can share with me?

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7503836325&fromMakeTrack=true#ebayphotohosting

Thanks all.

Sinarfar said:

Anyone know how to use this thing?

Click to expand...

When I was using a Sinar P2 in the lab.. this was the one thing that was "put aside" and went unused. If my aging memory serves me well enough, the "cap" was placed into the subject plane of focus and the "pencil" part was held against the ground glass as a rough measure measure the "magnification of the target".

I found it a LOT easier just to place a ruler in the plane of focus and compare against the metric grid on the ground glass.

Ken