IN his letter to you (Oxford Mail, June 14), Ken Roper states that, having spent most of his working life in the motor industry, he knows that the maximum limit allowed for a speedometer is three per cent over 30mph and nothing below.

What a pity that he is almost completely wrong.

Regulation 35 Road Vehicles (Construction and Use) Regulations 1986 plus EC Regulation (Community Directive) 97/39 and ECE Regulation 39 state that a speedometer must not under-read, as he says.

However, they go on to say that between 25 and 75mph it may not over-read by more than 10 per cent plus 2.5mph. So at a true 49mph it must not read higher than 56.4mph(49 +4.9 +2.5).

So, 56 could read 64, and 64 could read 73 (72.9 to be pedantic) and 70 could read 79.5.

This is all a lot higher than Mr Roper thinks and is all perfectly legal.

To take one example of the difference between his mistaken limit and the legal one, he could be driving at an indicated 57.7mph (56mph plus his three per cent) but if his speedometer was on the upper limit of legal over-reading, he would be travelling at a true speed of 51.33mph. This is somewhat less than the governed speed of an HGV, which is 56mph.

CLIVE BOWER Henwood