Speedo gauge: Miles per hour vs. Kilometers

I would think the speedo mechanism would be the same but the odometer portion would be geared differently. All it would take for the speedometer would be a different decal. I remember when vehicles here had both on them (Maybe the cheaper ones still do?). On Smokey and The Bandit, remember when Sally Fields looked at the speedo & asked if they were really going 100? If you looked at it, she was referring to the KPH section. The MPH was about 62.