Hi Jason, I can’t find anything in search, anything about Offen bore gauge, your assistance please.

what’s confusing is that anything on the datum line added to 10ths above the line always equals 9. The photos show this.

Thanks for finding the threads Bill. Yes, I started these threads, one about the shardlow mic but the Offen one didn’t continue to tenths. Michael G sent the copywrite docs, but these don’t explain tenths either.  One of my photos with datum at 5 is slightly out of parallax. Strangely, having both cataracts done, I can see that the tool must be rotated to see the exact position of the top line even though they’re only 3/16″ apart. The upper line is there for some reason and on datum zero, it reads 9. Maybe the tool only reads to 2 tenths, but why the line? Going to 9 strongly suggests a vernier scale but there’s no scale at the line!! Move the thimble anywhere and nothing correlates to a vernier number. I’m mystified but enjoying trying to fathom this out. Graeme.