There are indicators on your tires.

[color=#000040][b][url=http://users.skynet.be/derijprof/slijtageindicator.htm]Here you can see an example.[/url][/b][/color]
[size=85](Source: [url]http://www.derijprof.be[/url])[/size]

I have read that sometimes the examineer ask to measure the tread depth, I know it should be 1.6mm

But how can I measure it? Do I need a device for that in the car??