The MPM4000 active meter circuity allows direct readings of power output from the power amplifier it is connected to.
The meter scales, both wattage and decibels, are accurately calibrated when there is a four ohm impedance loudspeaker connected to the power amplifier the MPM4000 is monitoring.
I don't think it's easy to find meters for wattage & decibels.
Wattage, maybe can find la....for for normal AC power usage, and not useful for audio usage