The speed trigger points for cameras that most police use are noted as " guidelines" within a form of code of practice type documentation.
In Dyfed-Powys they wrre 10%+ 2 mph.
The reason they have this allowance is mainly twofold
10% for speedo inaccuracy.
+2 for a common sense allowance.
Speedometers are not permitted to read low but are allowed +10%.
That has been in force for some time and is well known to kit builders for the IVA test.
I just wonder when it will be tightened up by the introduction of suitable GPS systems.
Next time you use your satnav compare its speed reading with your car speedo.
