I play with metric just because I know it is more error-free than imperial, but since my method for manual targeting does not involve measuring and plotting on the chart, I almost never notice I'm playing metric. Only when taking the ship's length for speed can I notice it, but normally I make an estimate and then fiddle a bit with the position keeper instead of using the stopwatch, so it's only on rare ocasions I see I'm using different measurement units than intended. Anyway, despite being european and well used to metric, I never had problems using imperial, probably because my first real sim was SH1 and I got much used to it quickly.
