Why should the resistance of an ideal voltmeter be infinite and of ideal ammeter be zero?

Explanation

A voltmeter is used to measure the potential difference across the two points of a circuit. For it, the voltmeter is connected in parallel across those two point. The potential difference measured by voltmeter will be accurate if no current is drawn by voltmeter. It will be so if the resistance of voltmeter is infinite. Then the voltmeter will be ideal voltmeter. Thus, ideal voltmeter has infinite resistance.
An ammeter is used to measure the current in the circuit. For it, the ammeter is connected in series of the circuit. The current measured by ammeter will be accurate if there is no change in current of the circuit by the use of ammeter in series of circuit. It is possible if resistance is called ideal ammeter. Thus ideal ammeter has zero resistance.