Howdy a sdharlow!
I've made several DIY "hardness" testers over the last 40 or so years,can't find any of them?Now,it's how much flex a Lyman 450 exhibits when running nose dies.
The round ball indent measuring,even with reasonably sophisticated metrology and illuminated "glass",isn't without issues.Irrespective of how the indent was made....... enter long boring discussion here.
The irony for me,and this is just how I see it,everyone's a little different...... but,still using the ball bearing as the "probe" or tip,measure the handle in degrees of swing to achieve either, a known depth or predetermined force( bathroom scale,just don't use the wife's?) of the tip.... is a more acc qualifier than trying to mic the edges of a crater?