Correct method of nose-weight measurement?

If your car manual says max weight on the tow bar is 75kg then that is the max nose weight you can have.  You are not measuring the caravan nose weight correctly.  The caravan should be almost level when you check the nose weigh.  So the easiest way to do this without a specialist nose weight gauge (which a lot of people have - look at the Milenco one) is to get a piece of wood (a hammer handle might do!)  to allow the caravan to be almost level and put this under the hitch socket on the caravan and on the scales.  You should aim to get it to as nearer 75kgs as possible.  Remember must be with the caravan loaded ready to go.  It is trial and error but you will get there.

To ease the up and down motion try to load the caravan with little of weight at the front or rear.  Rule, heavy stuff low down and over the axle, light stuff at the ends.  My outfit has a 100kg limit and I run it at 95kg+ with the awning, cable, aquaroll etc in the car.  This subject is covered in detail in the Club handbook.

Noseweight should always be measured with the hitch at the same height as when the caravan is hitched to the car.

So - i need to get the hitch of the caraven at the imaginary height of being attached to the towbar?

So, lower the jocky wheel until the hitch is at that height?

See what the weight is on the bathroom scales I'm using?

And if I'm wrong, why is this so complicated????  I'm not completely stupid, i have 2 degrees!

You need three degrees to make it in the charts.

But are they in levelling a caravan!  Do what you say, measure the height of the tow ball, no need to imagine it, then place your hammer handle or piece of wood into the tow hitch on the caravan, other end on the scales and lower the jockey wheel until all weight on the scales. Then adjust the loading in the caravan to get the correct nose weight.  75 kg nose weight is very light, mine is 100kgs, and I usually tow at 95kgs.  You may have to almost empty the front storage; is the spare wheel there - out, cable there - out, ground sheet - out.  Anything to reduce weight at the front of the caravan.  Gas bottles could be a problem!  You have to careful not to put too much at the rear in order to avoid the pitching effect.  Once you have hacked it you will be ok for the future.

when was the last time you saw them though?

 I have a W4 noseweight gauge, it is hopelessly inaccurate, so to calibrate it I stood it on my very accurate bathroom scales when I first bought it and put an indelible mark on the W4 at my desired 85Kg. 85Kg being well within both the caravan and the cars noseweight limits.

To then use it, I place it on a block of wood, so it sits at the height it would sit when coupled up to my car. On my first trip out I adjusted things within the caravan to hit the mark exactly, on subsequent trips I have simply loaded up as I did for my first trip and found it within 5Kg, so near enough. Now I only check it occasionally, or if I make some changes to what I am carrying. 

Food goes in both left and right cupboard, clothes are about the same every time - All that can usually vary is where on the floor the awning goes and that sits over the axle.

Yes, the noseweight as measured with the hitch at the height it would be, when coupled up to the car. When coupled up, my towball drops down about 1/2" so I allow for that. 

The reason why you measure the weight with the hitch at tow ball height, is that if the hitch is lowered the caravan's noseweight will increase quite rapidly. Raise the hitch in the air and the noseweight becomes much lighter.

It also needs to be measured at the actual hitch - the socket where the tow ball goes, not at the jockey wheel. Measured at the jockey wheel, it would be somewhat less than the actual noseweight, because you will be measuring nearer the pivot point / the tyres.  

I am not sure that I understand why the weight at the hitch would change that much as it is raised or lowered. Surely a few inches up or down wouldn't make much difference to the weight at the hitch.

Well, it certainly does, believe me.

Simple way to prove that point to yourself, is to weigh the nose weight on a set of bathroom scales with the nose close to the ground, then again with the nose as high as you can get it.

The pivot point is the tyres, with the bulk of the caravan above them. As the nose is raised, the weight of the bulk transfers to the rear of the pivot point and the nose becomes lighter. 

By simply moving the really heavy items to the rear of my caravan, I can simply heave my caravan's nose up in the air manually, without resorting to jacks and have it sit nose up on it's rear corner steadies. The higher I lift it, the lighter it becomes. That trick is handy for any work I might need to do under the floor at the front of my caravan.