After looking at them and comparing, the one at healtech apprently shows the Speedohealer calibration value (the -22.5%) which is not really the speedometer error. It also bases it on a new tire, the one I used bases it on a mid-wear tire (and you can adjust it). Set it to zero and you'll get the SH calibration value of -22.5%.

Interesting that a company would have two different ones.