Nick.....if you leave the jockey wheel touching the ground it will be supporting some of the weight of the nose of the van, so no way are your scales going to give you the correct reading.
If you are using bathroom scales and a length of wood then the thickness of the scales plus the length of the piece of wood should be such as to support the hitch at the same height as when it is attached to your towball. Ideally the van should sit level when being towed.
If you have a proper nose weight gauge then procedure described by John (putting the gauge on a trolley jack and jacking it up until the hitch is at the correct height) sounds good, and slightly easier than putting pieces of wood under the gauge.
With both of these methods you must have the jockey wheel wound up, and it forms part of the noseweight too.
An easy way to measure, although not 100% accurate, is to place your scales on smooth level ground under the jockey wheel and wind up or down until the van sits level. This will give a slightly high reading.
Have you also checked the accuracy of your scales with a known weight?
And ideally the brake on the van should be off, but the difference this makes is not that significant.
------------- Jennifer
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