I think this
roller wave gauget could be translated as
"indicador del nivel de ondulaciones" according to your own expression that it is used to measure the level of the waves but for what I understand it could also be used to measure how the waves are flatened (roller wave)? in the glass? perhaps?
If so, then it could be translated as
indicador del nivel de alisamiento de las ondulaciones or something like that. I am not so convinced with the word
alisamiento but I don't really know what is the right word to explain the process of "flattening a wave".
Hope this helps...
