If the Tomos speedo goes to the pin you are going some undeterminable number of mph, just like when it says 40 you are going some undeterminable number of mph. The stock Tomos and Puch speedos are both wildly inaccurate.
When I'm going downhill on my Murray the speedo bounces between 40 and off the top end, and I know by pacing cars it won't get up past 35 actual mph.
On my Tomos, where I want to know the #'s of what my mods are doing I have a Trailtech Vapor. It was a bit of wiring, glue a magnet to the wheel and point the sensor at it, plug in the proper tire diameter, but pretty easy to install. Dead accurate mph readings, numerical tach updates every half second or so and the (digital) analog tach updates real time as far as I can tell.
I really need to get a picture of it up, it looks really nice. Also need to get the "Vapor" text off the front of it and paint the case to match the rest of the ped, then it would look amazing.