I'm having a go at Croc's 100 year old Polish Rye from the recipe section live before your very eyes.
Still mystified by the starter instructions: 1.5 Litres from 0.5L water + 0.5L rye + 1/2tsp salt.
Measured and weighed them. 0.5L of water is 500g (as you would expect). 0.5L rye came out at 300g.
Mixed they make about 0.75L.