[Shop-talk] Inside/outside angle finder

[Randall]

> I purchased a "protractor" or "Inside/Outside Angle Finder"
> 
> http://www.harborfreight.com/web-exclusive-sale/multipurpose-a
> ngle-finder-1028.html
> 
> I'm trying to figure out how to read it.  The main protractor is in 
> 5deg increments. 

Are you sure about that?  The photo on the HF site doesn't have enough
resolution to be sure, but I think I see lines every degree on the fixed
main scale, with longer lines for the 10 degree marks.

So, first you read the appropriate number revealed in the window, then count
the number of lines from the matching longer line to the "0" line on the
vernier.  Adding those together gives a reading in degrees.

To get finer resolution, you look either right or left on the moving
vernier, to find the mark that lines up closest with a mark on the main
scale.  The vernier has marks every 10 minutes and it's legend is in
minutes.  So that value in minutes (1/60 of a degree) gets added or
subtracted from the value above.

But I'd be surprised as all heck if that thing is really good to even a
degree, let alone 10 minutes.  The pivots look to be simple rivets, not
exactly precision components; and polypropylene is not exactly the most
dimensionally stable material in the world.  I note there are NO accuracy
specifications given <G>

Randall