Yep, my Autometer one is similar. There's a pulse sender that attaches to the 'box, which you should probably be able to get for whatever box you have if the one supplied doesn't fit.
With mine, you simply drive a known 2 mile distance in 'program' mode, and it calibrates the speedo. Change the gears, tyres, whatever, simply re-do the 2 miles - simple.
