1. The problem statement, all variables and given/known data Hi. I have a function that contains 4 variables: Q, R, [itex]\mu[/itex], dp/dx I wish to choose 3 of them, such that they cannot be combined into a dimensionless product. I have chosen (correctly) R, [itex]\mu[/itex], dp/dx and I would like to know if my method sounds correct: If we know the dimensions: [R]=[L] [[itex]\mu[/itex]]=[ML-2T-2] and [dp/dx]=[ML-1T-1] and I know that in order for them to be dimensionless, their power product must equal zero: [L]a[ML-1T-1]b[ML-2T-2]c=[MLT]0 or the system a-b-2c=0 b+c=0 -b-2c=0 By inspection, this system can only be satisfied if a=0 but that does not make any sense since R is a physical quantity. Hence I have reasoned that these 3 variable cannot form a non-dimensional parameter by themselves. Does this work? Thanks!