What is the relative resistance of a good ammeter? A good voltmeter? Why?

Question

What is the relative resistance of a good ammeter? A good voltmeter? Why?

Answer 1

Relative means, I assume, relative to the test circuit. A voltmeter should have a very high resistance relative to the circuit resistance, at least 100 times for a 1% error. Ideal voltmeter has in infinite resistance, and 10MΩ or 100MΩ are common.

Why? if the resistance is lower, it will load the circuit and change the readings, and therefore the readings will be inaccurate.

An ammeter should have a resistance lower than the circuit it is in, at least 100 times lower for a 1% error.

Why? if the resistance is high, it will change the circuit and possibly change the readings, and therefore the readings will be inaccurate.

Answer 2

for an ammeter, your measuring current.  you don't want the meter itself to influence the measurement so you would want an ammeter with a very low relative resistance.  that way you'll know that the current you're reading from the meter is essentially the circuit current not the current required to drive the ammeter.

for a voltmeter, your measuring voltage and similarly, you don't want the meter itself to influence the measurement so you would want a voltmeter with a very high relative resistance that puts less of a burden on the source being measured.