What's more accurate, a speedo or satnav?

[Kj159]

What do people think will be more accurate, a 15 year old Polo speedo or a satnav that is a few years old?

Speedo reads 70 - satnav reads 65
Speedo reads 80 - satnav reads 73
Speedo reads 30 - satnav reads 28

etc...

Would like to know which one to go by when it comes to speed cameras and things

[kambites]

At reasonably constant speed on reasonably flat roads, the sat nav . If your speed is varying significantly they're probably both rubbish.

[eybic]

Satnav will be more acurate, it will generally be 10% slower than your speedo reads which by the figures you give seems to be true.

[catman]

Satnavs are supposed to be accurate to around 0.5%

Tim

[Schtum]

At a steady speed on a straight and level road, the GPS unit will undoubtedly be more accurate. Note, however, that the GPS signal updates at a frequency of 1 Hz; so any sudden changes of speed i.e braking in a 15 year old Polo, rather than acceleration won't register instantly.