i think i can say that when used properly the tool is accurate. tried a few different feeler gauges and all within .001
the range on one quarter of the rotor seems to be about 1.42 to 1.57. i guess i do in fact need a new rotor. distressingly short life - 2400 miles!! the .15mm variance doesn’t seem to affect the actual braking.
boring video - which does illustrate how much the measurement varies if the 1/8” diameter (approx) flat head of the micrometer isn’t completely true and flush on both sides. the tool has a very soft clutch, so cranking it with the dial doesn’t exert enough force to square it up.
https://imgur.com/a/X2KJHNk