I don't trust any of the commercially sold gauges.
Of the ones I have seen
· The graduations are rather coarse
· Their accuracy cannot be easily checked (even though the milenco claims to be calibrated – that does not last forever, and how do you prove it,
· The length or height of the gauge is not adjustable.
The towing regulations require the ‘imposed’ nose load on the tow vehicle to be measured. This may sound simple, but when you appreciate that for any given loaded caravan the nose load actually changes depending on the height of the hitch above the horizontal then you realise that the actual nose depends on how much the suspension allows the hitch to fall when the caravan is attached.
For single axle caravans the nose load decreases as the hitch is raised and increases when it is lowered. Twin axles are more complex, which makes the correct measurement even more important.
So to accurately measure the true nose load, you have need to have the car and caravan on level (Horizontal) ground. Both the car and caravan need to be fully loaded with all people and hitched together, so the suspension is settles to its driving height. The height of the hitch needs to be measured. Then the caravan should be uncoupled and the gauge fitted to the caravan hitch, and set the exactly the same height as when the caravan was hitched up. None of the commercial gauges I have seen are not adjustable so it will only be luck it it’s the right height!
So the method that uses bathroom scales and a cut length of wood is a better method, though care must be used to prevent it from slipping out or off the scales
The accuracy of bathroom scales can be relatively easily checked, by weighing an empty aqua roll, then filling with a specific number of litres of water, as water weigh exactly 1Kg per litre.