I would have thought that a "calibrated" BPM over a span of settings is all that is required for an ECG simulator. And that is something that can be done "in-house" by checking against some other piece of Certified kit, like an oscilloscope.

In my experience the content (shape etc.) of the waveform(s) vary somewhat (and sometimes by quite a noticeable margin) ... so unless there is some "British Standard Sinus Rhythm" (and then all the arrhythmias) then I guess we need to settle for what the *Bio-Teks of this world dish up.

* Other manufacturers of ECG simulators may be available.

We bought a calibration 'stick' for all the hight measures in the trust. I don't think we have ever sent it away for calibration. Do you think we should?

Just use your yardstick ... as the er, yardstick!