DMM hack adds fine analog resolution so you hear rising voltage as a rising audible pitch and allows eyes-off monitoring.
A DMM processes various inputs such as voltage into a ±200mV range for the internal digital meter.
I measure that internal signal with an ADC in the ATtiny85 CPU and use it to control the frequency or pitch generated by the CPU and applied to a tiny speaker.
Simply put, the audible frequency is lowest at zero input and increases in frequency as the absolute value of the magnitude of the input increases.
A self-calibration feature involves shorting the input while pressing a switch at turn on.
You can measure the resistance of a potentiometer and listen for lack of continuity while you turn the knob. Noisy potentiometers are very noticeable.
Will the accessory work in your DMM? Connect the positive input probe to the positive battery terminal. If the meter measures its own battery voltage at very close to +3.00 Volts, it will work with your D