DME-P is a modified version of normal DME (only used with MLS). As the name suggests, (P for precisson) it is more accurate than normal DME.

Microwave Landing System (MLS)

The MLS system uses separate transmitters producing two scanning beams (one in azimuth and one in elevation) and a precision DME (DME/P) which allows the aircraft to fix its position very accurately in three dimensions.

• When the DME/P is not available the MLS can only give a straight in or offset approach, more or less the same as an ILS.