@1 km is:
1000m
100m
10,000m

@1 cm is:
10mm
0.1km
0.01km

@250mm is:
0.25m
2.5cm
0.25cm

@0.5km is:
500m
50,000mm
5,000cm

@250,000mm is:
0.25km
0.025km
0.0025km

@15cm is:                                            
0.00015km
0.000015km
0.15km

@320mm is:
0.32m
3.2m
0.032m

@0.06km is:
600cm
6000cm
60,000cm

@0.84km is:
840m
84m
8,040m

@2km is:
2,000,000mm
2,000cm
20,000,000mm