Just trying to personally understand this is making me shed a few tears. Good luck with finding someone to answer your question!
Answer:

Explanation:
Let consider that velocity profile inside the circular pipe is:

The average speed at
is:


The velocity at the center of the pipe is:


Answer:
The operating principle of a ramp type digital voltmeter is to measure the time that a linear ramp voltage takes to change from level of input voltage to zero voltage (or vice versa).