Confirmed in the SR automatic I'm driving that the speedometer is consistently reading 4 km/h higher than the car's computer, which looks to me like a correction factor. I used an OBD-II scan tool (ScanGauge-e) and checked from 30-100 km/h:

Speedometer reports...
OBD-II value...
30 26
40 36
50 46
60 56
70 66
80 76
90 86
100 96

I didn't check against the odometer, but will do that too. I bet the dash display matches the OBD-II values.