What is the reed switch in the speedo for?

[1980cm400t]

I am redoing the wiring on my xs1100 and I noticed that there is a reed switch in the speedo. I found this to be strange given that the speedo is mechanical. Looking at the wiring diagram the white/green wire from the reed switch is supposed to go to the flasher canceling unit (which I have removed). What does this reed switch do? If I were to guess it would be that the reed switch keeps the cancellation unit from turning off the turn signal when you are stationary such as when sitting at a light. Can anyone confirm whether this is the case? (if so it is very clever) I have a 1980 xs1100 special model btw.

[BA80]

It counts speedometer head revolutions and sends a signal to the auto turn signal canceller.

[crazy steve]

Yep, the reed switch is one of the things that tells the turn canceller when to cancel. Don't need it if the canceller is gone....