touching the armature bar

When I am getting tattooed I've noticed the artist touches the armature bar with his thumb with the machine running before he starts lining or shading. Why is this? I've seen it many times, I'm guessing it is to check speed or power by touch, is this true? thanks

what you are seeing is the artist checking a couple of things here 1 stroke 2 hit artist is seeing how hard the machine will be hitting and driving the needle in 3 making sure machine is functioning properly under a work load i do it also its a good way to keep familiar with your machines