SMART FORTWO CABRIO Operating Instructions Manual page 56

Upper centre console
Function
The tachometer displays the engine
speed in units of 1,000 rpm.
The optimum engine speed ranges (rpm) are:
Driving off
Normal operation at constant speed
Brief periods of acceleration, e.g. when passing
54 Blind date
Petrol engines
1,000 2,000
2,000 3,000
3,000 6,300
Diesel engines
1,000 2,000
1,800 3,000
3,000 4,400