Here is a little, but so useful tool I made for measuring and setting up the string action gauge, which is the height of the string above the top of the frets.
This is something that must be really carefully setup, for a good and comfortable playability of the instrument.
There have been for a long time some US versions of that tool , missing the metric version, so I really did it for that reason. Now, I thing the commercial version also exists in metric.
The definition is the 1/4 of a mm.
I have an article about that, it shows the two versions I did of that tool.
It is simply something you can download on my site and print by yourself (verifying the accuracy of your printer) and then it's easy to fold it in the center line and then glue it, and even plasticize it.
La Belle Note - My Metric String action gauge