mrad
1mrad = 1 meter at 1km (ignoring initial beam size, i.e assuming its 0)
1mrad is considered baseline for lasers.
Anything tighter is considered a higher quality system. 0.4mrad is pretty much maxed out tightest possible
Consider too, that although a high value means your beam becomes bigger and less sharp visually, it does also mean its disipating its power over a wider area, so becomes less dangerous to eyes and skin over distance (although, often over a LOT of distance!).
Beware of 1mrad specifications on low cost systems….apparently, many cheap manufacturers will put 1mrad because they assume no one will check and it can turn out its actually quite a bit higher.
Beam divergence calculators
https://www.laserworld.com/en/laserworld-toolbox/divergence-calculator.html
