I apologize my last post (More on Sextants) had a typo. 0.18 nm does convert to 333 m, but then I switched to 320 m for some reason.
 
If doing the math with your students, I suggest changing all 333 m to 320 m, (that way the 10 m offset to 310 m makes sense). Therefore, if the radar was 320 m away, it would have read 0.173 nm, not 0.18 nm.