Liam, kindly sharing some of his strategies, posts this in the forum:
I can hook the tape measure on the edge of my laptop and measure as far as I need to. If you use a desktop some blue tack should be fine as long as you guesstimate how much of the tape measure you’re going to need to use first.
The full thread is here.
There are lots of creative ways to handle centimeter. If you get the mini version of the tailor’s tape (thinner, more flexible), you might attach it with a piece of sticky tape to a stationary monitor.
Or of course, two hands, measure it out.
I would love to see front facing cameras of cell phones be able to produce a reliable centimeter distance, but haven’t found anyone with a good way of accomplishing that. One day, I’m sure we will be able to dispense with the tapes, and reach for our phones for a quick centimeter result.
Thanks to Liam for taking the time to share and post the picture!