Question

Why don't we use the setting at the maximum or minimum point of the flowmeter to do measurements?

Does it give inaccurate results?

Answer 1

Most of the physical quantities are defined with respect to some standard quantities as measuring absolute values are always tough. See in case of Kelvin scale of temperature.

For a physical quantity measurement device we make up a scale using some standard quantity whose values we already know. This process is called calibration.

This scale generated by calibration process will measure between those scales only. If you are fixing the setting at extreme points then we won't be able to see one side of deviation. Say if you fix the maximum point as reference then the deviation above it can't be measured as there is no scale to measure it. Same can be said for minimum point also.

We usually try to find out the deviation from the desired value while measuring the quantity(here flowrate). So, by keeping the setting at min or max point we will lose the purpose as well as accuracy of the error by quantifying the errors.