I do not know why they did not put numbers on those gauges, I kinda hate them. I changed mine out to a gauge that has reference numbers so you can tell what it is running within the manfactures error of the gauge. it is a cheap improvement ,just remember to change sender and gauge if you use a electric one, which I do not believe a mechanical probe style will work in the machine anyway ,I do not believe they make one with a long enough sensor probe. I could be wrong about that.