Originally Posted by SlowerOne

I don't agree with that method. The tyres should be parallel to the arms of the vernier - 90deg to where you have them in your video.

Using the thin part of the arm only measures the tyre at that point, and it is easy to push into the foam giving a false reading.

Using the whole length of the vernier arm across the face of the tyre gives a more accurate reading, and allows you to see if there is any taper (fronts) or raising of the joint (rears) on your tyres.

Using the whole length of the arm also makes it easy to find the slightly larger of your 'pair' of tyres to put on the left (clockwise track) of the car when swapping tyres from side to side.

I see a lot of people doing things this way and they always end up making simple errors in tyre measurement due to the issues above. When shown the other way they all swap. HTH