It is the most important meter in the system. It is generally the largest meter in the system (certainly if you only have one production meter).
The cost of this meter is generally sizeable in nature compared to all other meters as well.
It is the starting place of all balance calculations and therefore should have the most activity against to the highest standard.
Since the cost of the meter is the greatest, even more care should be taken for the selection, installation, maintenance, and calibration prior to purchase.