The Axis is vertical to the middle of the impeller.

Above the shaft there is a small gear, and with it the decimal number of gear meshing, used to achieve the goal of the cumulative number of revolutions.

The "Decimal number gear" When the single gear is turned ten laps.

Ten digits gear turns in a circle. In other words, ten digits gear once over one circle. Single gear is active, turns the ten digits by it.