If you or know anyone with a set of weighing scales, you get on the scales, note the weight, pick up the bike, get back on the scales, note the weight now, the difference between the two is the weight of the bike.
No bathroom scales. I assumed they wouldnt be accurate anyway, but now I think about they are probably sufficient. I will invest!
Thanks very much for the advice. By the way, the japanese man paid 150 for an average cond super 4... not sure if he got carried away.. not even sure he is going to pay, as with posstage he's looking at 300 for a moulton that is in my opinion a very flwaed design, cheers.