Buy Used Oscilloscope Link
Connect a probe to every channel and attach it to the built-in probe compensation output (usually a small metal tab on the front). You should see a clean, steady square wave.
Look for a rate at least 2.5 to 10 times your bandwidth for accurate waveform representation. buy used oscilloscope
Professional refurbished units from manufacturers like Keysight are calibrated and often come with a warranty. Essential Pre-Purchase Tests Connect a probe to every channel and attach