An NMI M prefix tells you that the pattern approval document is mandatory and that it has been prepared by NMI, ie it is not based on a specific OIML international recommendation.
NMI M 1 Pattern Approval Specifications for Length Measuring Instruments
NMI M 2 Pattern Approval Specifications for Beverage Dispensers
NMI M 3 Pattern Approval Specifications for Area Measuring Instruments
NMI M 4 Pattern Approval Specifications for Milk Tanks
NMI M 5 Pattern Approval Specifications for Brake Force Measuring Instruments
NMI M 6 Pattern Approval Specifications for Electricity Meter (click here for an advance draft copy of the second edition which will take effect from 1 July 2010)
NMI M 7 Pattern Approval Specifications for Point of Sale and Weighbridge Transaction Systems
NMI M 8 Pattern Approval Specifications for Protein Measuring Instruments for Grain
NMI M 10-1 Meters Intended for the Metering of Water in Full Flowing Pipes. Part 1: Metrological and Technical Requirements
NMI M 10-2 Meters Intended for the Metering of Water in Full Flowing Pipes. Part 2: Test Methods
NMI M 10-3 Meters Intended for the Metering of Water in Full Flowing Pipes. Part 3: Test Report Format
NMI M 11-1 Meters Intended for the Metering of Water in Open Channels and Partially Filled Pipes. Part 1: Metrological and Technical Requirements
NMI M 11-2 Meters Intended for the Metering of Water in Open Channels and Partially Filled Pipes. Part 2: Test Methods
NMI M 11-3 Meters Intended for the Metering of Water in Open Channels and Partially Filled Pipes. Part 3: Test Report Format