HOLDPEAK Digital Insulation Resistance Tester HP-6688B 100V/250V/500V/1000V/2500V/5000V Voltage Test, 200G Ohms Megohmmeter 2000 Counts Backlight, Auto Ranging, Data Hold (Battery Included)

https://a.co/d/0iNbebp1 I use it at work for megging motors. It's no fluke but it was able to correctly read a 20 gigaohm resistor string I wired up. Having my leads resting on metal is enough to change the reading.