Settings and units (metric/statute)

I've started playing with the app settings in SDK 1.2.0 beta. My app, ballistics, supports inputting data in both, metric and statute units. Basically the watch checks the current setting, prompts the user to enter the data in correct units and then converts input into statute units that are used internally.

I am trying to move some of the less used configuration to app settings to save memory. After reading the available docs, I could not figure out how metric/statute should be handled in app settings. My initial idea is to just require the user to convert their data to statute themselves, but that's pretty bad UX. Other option would be to have an additional option "Unit type: metric/statute" and keep doing the conversion in the device but that does not seem perfect either.

Does anyone have recommendations?