I have a K40 Laser that does not have the analog meter but has a digital display and I have never cranked it up past 50. I am trying to cut MDF that is 1/4 inch thick and it doesn’t seem to cut. I am afraid to crank it up past 40.
I would recommend installing an ammeter permanently.
If not, you can temporarily install your multimeter to measure the current as a function of the digital power % . That way you can establish at what point (digital %) your tube current reaches about 15-16ma which the typical max recommended current for K40 tubes.
Of course for cutting issues you also need to make sure everything is aligned properly and that the focus point is set correctly.