Sorry you find it patronising but,why would a rgi ask these questions on a diy forum,surely an rgi would know how to test a basic domestic meter and instal,most would understand the r5 denoter isn't size.
To the say the time in this situation is always 2mins is wrong,the wrong guage could have you testing forthe wrong time,now lots of guys use the Regin premier guage but that alters alsorts of things when comparing it to a water guage or digital,plus lots of domestic jobs now have massive iv due to the u16meter being not far off of the domestic volume threshold,finally the fuel is just as important.
Just found it all to be thbwrong place for the question,with wrong satements for answers.it was your username that led me to be so......with my replies as all of the abov is basic gas stuff regardless of how long a gasman.
John your not old,just young in retirement.