Helicopter pilot inadvertently entered a TFR while using a GPS device calibrated in statute miles instead of nautical miles.

Narrative

I was the pilot in command of a lifeguard helicopter. I had a flight nurse; flight paramedic; and patient on board the helicopter. I was taking the patient from a small rural hospital to a specialized facility. During our shift briefing we brief with the crew any TFR's that might pertain to us. I briefed with the crew that morning that the local AFB would have a TFR in effect throughout our shift at an altitude of 1;600 FT to 18;000 FT. I noticed my flight path would take me close to that restricted airspace. As I passed by the airspace I made sure I was greater than 10 miles away from the AFB. As I was landing at the hospital I was told by the Tower to contact local Approach Control. I called Approach Control and spoke with a lady that asked me if I had just flown through the TFR. I told her I had remained greater than 10 miles away. She told me the Controller told her I had 'clipped' the corner of the restricted airspace. I asked her what I needed to do. She took down my personal information and said she would be forwarding the information to the local FSDO and I should expect a call from them in a couple of days. On my 45-minute flight back to base I was racking my brain trying to figure out what had happened. As I was looking at my GPS I noticed the GPS I was using was in STATUTE miles not nautical miles. At a distance of 10 miles my error could be as large as 1.15 miles! Lessons learned: Make sure you are comparing apples to apples and oranges to oranges. Distance given in TFR's are given in nautical miles make sure your are measuring distance in nautical miles not statute miles.