Descriptions from the IEC website:
IEC 61987-12:2016 provides an operating list of properties (OLOP) for the description of the operating parameters and the collection of requirements for a flow measuring equipment and device lists of properties (DLOP) for the description of a number of flow measuring equipment types.
IEC 61987-13:2016 provides an operating list of properties (OLOP) for the description of the operating parameters and the collection of requirements for a pressure measuring equipment, and device lists of properties (DLOP) for a range of pressure measuring equipment types describing them.