PDOP

From DictionGloss

Position Dilution of Precision, a figure of merit (used without units) expressing the relationship between the error in user position and the error in satellite position, which is a function of the configuration of satellites from which signals are derived in positioning (see DOP). Geometrically, PDOP is proportional to 1 divided by the volume of the pyramid formed by lines running from the receiver to four observed satellites. Small values, such as "3", are good for positioning while higher values produce less accurate position solutions. Small PDOP is associated with widely separated satellites.

PDOP Mask - Usually a user-definable upper limit for the PDOP you will tolerate during collection of a dataset. If PDOP rises above the pre-set limit, GPS data collection will be suspended until the PDOP decreases below the limit.