Why a high input impedance device is generally needed to measure the hall voltage?

A high input impedance device is needed to measure the Hall voltage to minimize the loading effect on the circuit being tested. Low input impedance can draw significant current, altering the voltage distribution and affecting the accuracy of the measurement. By using a high input impedance device, the measurement can be taken without significantly disturbing the conditions of the sample, ensuring a more accurate representation of the Hall voltage. This is particularly important in sensitive measurements where precision is critical.