The third segment of the EL code specifies the type of rooftop precision result that has been returned. This only applies for EL codes where the Geocode Precision is 5 ('rooftop level - interpolated or address point'):
P - Address point precision: the geocode (latitude / longitude) coordinates have been taken directly from the data provider's data
I - Interpolated rooftop precision: the geocode (latitude / longitude) coordinates have been calculated by interpolation of street segments in the data provider's data
For other Geocode Precision levels, the third segment of the EL code is not used and will always contain 'F'.