if you get two clocks set you have to nom your no 1 clock the other clock can only be used in the event of your nom clock being way off time or stoplng ten you can time into no 2 or if rubbers are in clock 1 allready you can open the clock in the presence of another member remove rubbers and time into clock no 2 allso duplacate rubbers go in no 2 clock and both clocks returned to clock setter thats the shu rule