What is the only appropriate way to write "units" of insulin for example to avoid errors while reading the script or note?

I.e 55 units daily: In the us, Insulin is counted in unit rather than milligram(metric system), thus to avoid confusion and reducing error, write as legibly as possible and spell-out the unit word following the number such as Levemir (insulin detemir) or Lantus "55 units" daily etc.. Consult doc/your pharmacist for clarification, if needed. Good luck.

Insulin RX: Name of insulin sig: # of units per day # of vials refills: # or duration of refills this should do it for the pharmacy.