I bought one only and it was simple to switch from side to side with bike idling. I see no need to buy two.
The reference numbers are just a relative guide.
This is an easy tool to use and I would recommend it. Michael
I was in Italy at the Imola race track where there was a scambio going on. There was some very expensive multi cylinder bike being started up. there was an old timer helping with some issues tring to sync the carbs on a BENELLI He installed 4 round popcycle sticks in each carb with the engine turned off... slowly rotated the throttle to see the movement of the sticks and adjusted them so they all moved down a the same time evenly...Lots of people looking on.. OLd school tuning . quick ..down and dirty and very effective.