Working pressure and pressure drop across system

I asked this question few weeks ago but still confused.
Im quoting some of this from a book.
Test for regulator working pressure at meter 'Turn on ONE appliance at full rate(lets say cooker)' should read 21mb+/- 2mb. (For arguments sake say pressure was 21mb). It then says with ALL APPLIANCES RUNNING there should be no more than 1 mb drop between meter outlet and appliance. Therefore inlet to all appliances should be no less than 20mb. But would the regulator maintain this pressure of 21mb with all appliances running.
To sum up if 21mb at meter with cooker on it should it be 21mb with all apps running?
When I have tried this the regulator as dropped to 19mb with everything running. Can regulators compensate 100%. Is this where the tolerence comes in (21mb+/-2mb) with one app on and then you allow for 1mb drop across system or maybe 21mb and allowed to drop to 19mb with all apps on. Im a trainee and nobody can seem to find my answer.
Thank you very much everybody.

Testing with a cooker on 3 rings is a bit old hat now and a last resort.

If say, a combi was fitted, you would test with the combi running flat out on hot water. The only time I add extra appliances to the test if the combi is only running at 20mBar at the meter.

I know what the current regs are, but if I fit or have a combi to service and find it is running between 19 and 20 mbar I still call it in as a pressure problem. I like all my regulators to run at 21 to 22 mbar WP.

The regulator should compensate for for additional or less load that is its job as a 'regulator'.

Regulators do go faulty and can stick, I've lost count the number of times I've had them changed by NG.

The pressure drop you are citing could also be caused by inadequate pipe sizing to each appliance.

Strongly suggest you'd be better served in "The Combustion Chamber".
Tell admin you're a trainee. I would hope he'd let you in!

Ant101 you're right, it's called "droop" and nothing's perfect, despite what Corgi think.