Mises says we have to define velocity

Says Mises, according to Frank Shostak:

But it is absurd to dignify any quantity with a place in an equation unless it can be defined independently of the other terms in the equation. [emphasis in the original]

The subject is money velocity, how many transactions do we have over some fixed time period.  Nice enough definition.  Is it important?  You bet, it tells you how many clerk stations to build for a new store. If shoppers arrive at a certain rate,  then you want to know the  rate to compute the number of clerks being employed.   Money velocity gives us a general estimate.