Most flow signals are normally regarded as rate signals. For example the Speedometer in your vehicle  whether it is a needle or a digital device will go up and down according to the actual speed you are going

When your car stops the speedometer goes to zero. It is the same with the flow meter, when the flow rate stops the flow signal goes  to zero

However, the ODOMETER or rather the milage counter reads reads the total number miles that has been driven. This can be compared to a simply to a flowmeter totalizer

For example the flowmeter display  fig 4 is indicating the flow rate on the counter above and the flow total in the display

Fig 5 shows the total amount of cubic meters consumed by a home user. In the above case it is 2983 M3.  This information is useful to a domestic water supplier billing department because their job is normally to bill the consumer for the actual amount of water he has used irrespective of what hour of the day he used it.

However, the water company may also want to know the actual flow rate in larger water distribution pipes during particular times  of the day to calculate the load, since water users tend to use water at the same times .e.g people taking a shower  before going to work

Totalizers are also important if someone wants to deliver a fluid in a batch e.g  if  100M3 of product has been promised to a client the batch controller will send a signal to the supplier’s pump or valves to stop delivering the product as the client requirement has been met.

Batch control is also used in many factory processes .