How to use a digital multimeter to measure large resistance

How to use a digital multimeter to measure large resistors
When measuring resistance with a DT-830 digital multimeter, when the measured resistance value exceeds 20MΩ, the meter head displays "1", indicating that the resistance value is beyond the limit and cannot be measured.
There are many methods to measure large resistors exceeding 20MΩ. Here is a method that is based on the principle of resistor parallel connection to briefly measure the resistance value of the large resistor being measured.
The measurement method is shown in Figure 2-1. First find a resistor R with a suppression resistance value less than 20MΩ (required to be close to 20MΩ, such as 18MΩ), and connect it in parallel with the digital multimeter. This is the precise resistance value of R that can be measured with a digital multimeter. Then insert the resistor to be measured into sockets X1 and X2, and the digital multimeter can display R and RX, and the resistance value R# after parallel connection. According to the following formula:
R#=R·RC/(R+RX), it can be deduced that:
RX=R·R#/(RR#)
can be used to calculate the resistance value of the resistor RX to be measured.