I believe something similar happen to someone else on the forum.
If you want to know if the hour meter is active when the switch is on, just turn it to the on position for about 1 hour and then check the results.
You can not reset it, but you can unhook the meter for the amount of time you desire to correct the true tractor usage.
I am not saying to do this , but some people will disconnect the hour meter in order to show less hours on the tractor, and then hook it back up when they sell it. There is no way to tell, unless there is a hidden meter some where on the tractor. The rental business is aware of this practice. Some of them can monitor the running time on their machines remotely and know exactly where the machine is.