how to change units on graphes

hi,
I’m graphing signal strength on my mikrotiks routers (using snmpwalk on the device/create probe on the oid). Then, when i pass the mouse over the device i see the graph of what i’m probing. But actually, it seems to use “ms” as default unit and i would like to have dBm for signal strength and on a different graph. How to do this?

many thx.