## Channels, and what you actually need
Channel count describes how many leads print simultaneously, not how many electrodes are attached — a 3-channel machine still records all 12 leads, it just prints them in groups. For a general clinic that is usually enough. A cardiology practice or an emergency department wants 12-channel, because a simultaneous 12-lead trace is what lets you compare across leads at the same instant.
## Verify it against a simulator
An ECG machine should be checked against a patient simulator, not simply switched on and tried on a member of staff. A healthy volunteer produces a normal trace on a machine with a miscalibrated gain, which tells you nothing. Ask for the calibration check at 10 mm/mV and the paper speed verified at 25 mm/s.
## Leads and paper are the running cost
Patient cables and limb leads wear out and are the most common cause of a noisy trace being blamed on the machine. Confirm what cables are included and that thermal paper in the right size is available locally — it is a small thing that stops a clinic when it runs out.