In England if my Drager breathalyser gives a high result of 510mg/ml of alcohol from lungs straight after drinking 5 units and 34 mg/ml 40 minutes

The second is accurate.

@ArishMell The false reading which he had the first time is not the fault of the Chinese. He took the breathalyzer “straight after” drinking. The alcohol hadn't made it to his lungs. He says the second was 40 minutes after the alcohol, and that is a good time. Even better than 20 or 30 minutes.

34 micrograms from 5 units after 40 minutes sounds just right, especially if it's liquor.

Not necessarily.
Alcohol coats your mouth, tongue, oesophagus, and will directly gas off from all these surfaces giving a high reading immediately after drinking.
Ie: direct undiluted gas transferrence.

With variability, any drug that you digest, you frequently lose half its effectivness just from the act of digestion. It then goes to the intestines and liver, which starts processing it slowly. Only THEN does it get into your bloodstream, and then after circulating around a bit, difusing into your lungs.

So although you have drunk x amount of alcohol, a fair whack of it is in different parts of your body still being processed and only some of it has reached your lungs.

Make sense?

It might be if by "my breathalyser" you mean some cheap kit you found on Amazon - made in China, untested, not calibrated.