The program can be toggled between the English (inch, grain, foot, yard) and the Metric (centimeter, gram, meter) systems of measurement. Traces are saved to disk in whatever system is currently selected. When traces are loaded from disk they are converted, if necessary, to the currently selected system. The conversion is accurate to six significant digits, but because trace parameters are rounded off, some amount of error can be expected if you change to the other system and then change back again.
Note that when using the English system the scale can be in either yards or meters.
Click Options on the main menu and then click English/Metric system. Another menu opens with the following options:
The currently selected option has a checkmark beside it. Click the option you want to use. The program displays another window that gives you a chance to cancel. If you click OK, the program exits, but will use the selected system when it's next started up.