Does anyone know how to interpret ruse and wuse counters in /proc/partition?

I was bowsing the linux kernel code and could see the link between rd_ticks in hd_struct. It looks as if this counter is incremented by the relation between wr_ticks and number of ticks in the past IO read request. So is wuse linked to wr_ticks in hd_struct. But when are rd_ticks and wr_ticks reset? If they are not reset I guess these unsigned ints will overflow to zero and carry on from there? Is this the way it was intended?

My big intention is to measure % disk busy times and that is where I think ruse and wuse may help.