Switching from Km, to MPH.

The ratio is .62
But there are not enough pinions to make this switch using the MPH speed-o. I tried it.
What you need is a Multiplier/reducer, adapter like the Gear-Vendors unit..
What you do is get a really short cable and drive the unit, the stick your cable on the other end. Presto. If the internal ratio of the unit is not exactly correct, then you change your pinion, by calculating the percent error.

Here is an image I grabbed off the net;
OOPs it won't paste
Here is the link
https://encrypted-tbn1.gstatic.com/...7SYQnAeQNMJCZfoTQJqVhHWxP46dGQBrT527ssc69JS8w