Flow meters are usualy built in and auto adjust. Checking flow with a rotometer is fast and simple.

Most meters operate under factory calibration factors that are acceptable under most conditions. You can, but are not required by any regs, to set user calibration factors based on local conditions. This is a very tedious process that you don't typically see people do unless they are in abnormal conditions like constant fog or whatever. On my meters temp and pressure sensors are built in, no idea about the purple, but I would trust the particulate data if it passed a flow and zero check.