Should be GPM.

I have the Koolance VL3, the CPC for 3/8" ID (APC series?) and the 1/2" CPC NS6 series lying here. The Koolance are noticeably better than the 3/8" CPCs, but the 1/2" CPCs have a completely different construction, and I haven't tested those yet.

I'm gonna publish results flow for all of them once I get my proper rotameter, I currently have a Digmesa FHKUC but I noticed that the absolute value is not correct, and I'm not sure whether the relative values are correct either.