Anyone know what this is for?

[93Festiva]

Hi everyone. I've got a 1993 Festiva WA that I recently swapped an Australian market cluster into. Everything works, but according to a GPS speedometer the cluster speedo is out by roughly 12 km/h at about 50 km/h. I am running the stock 12" tire size, and noticed on the back of the speedo that there is a metal lever on one side that can move into 3 different spots. Does anyone know what it is for and know what position it should be in? Thanks in advance!