** IN DEVELOPMENT **
Regarding how a compound meter works, it’s actually relatively simple. Most resources online over-complicate it so it seems confusing.
Essentially, a compound meter is two different metering technologies in a single meter:
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Low Flow Conditions: The low-flow side of the compound meter uses positive-displacement technology… like a diaphragm meter for example. Positive Displacement (PD) meters are very accurate and reliable at lower flow rates and it is resilient for long-term usage because they are less likely to gum up from mineral deposits which is another reason why they are used for residential homes.
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High Flow Conditions: The high-flow side of the compound meter usually uses turbine technology. During high flow conditions, the water bypasses the low flow side because it pushes the diaphragm beyond its physical limitations. Basically, it spills over to the high flow side of the meter because the low flow diaphragm meter starts to struggle from the pressure of shoving too much water through it. The downside of turbine technology is that water can move through it at very low flow without being detected, so it is very inaccurate at low flow.
Combining those two technologies allows a compound meter to measure volume much more accurately across a broader range of flow rates, as well as conditions where flow rates fluctuate abruptly.