Ok, last night I checked my 1litre jug against my 5litre jug and there was a discrepancy.

I then weighed the 1 litre and it was short of 1kg by 25 gramms which means that if my scales are accurate then I would end up with approximately the same results as you Dan whereby the dipstick will be out by 1 litre if extended to 40 litres.

That then would mean that by using that measurement you would be actually be 800 mls less water in a total of 32 litres, and that would give you a higher mash efficiency than what Beersmith predicted as the total volume would be less than The BS formula. This makes your observations correct in the above posts. I was having trouble getting my head around these figures late at night and before rushing off to work yesterday.

My figures above are only based on the results of my scales.

So, in hindsight, there is then a few morals of this story,

Don't automatically trust a measuring jug even if it supposed to be industry accurate.

Use accurate scales and weigh water for volume measurement for total brewing water accuracy.

Don't trust any dip stick made by Dicko as they are proven to be innacurate.

I hope this helps anyone wanting to calibrate accurately a sight glass or dip stick.

Cheers