Analog output meters
Meters with analog outputs are designed to measure flow.
Output is typically a voltage (0-10V is common) or a current (4-20mA). The markings on the meter should tell us what the output scaling is (for example 20L/s@10V).
By monitoring flow over time we will get an estimate of the volume, but please note that this method is not as accurate as using a volume meter as small measurement errors accumulates over time.
Therefore flow meters with analog outputs are not recommended for billing purposes.