The Ca figure is available calcium and the Ca0 figure is alkalinity/pH raising ability expressed as % of CaO. When you look at typical fertiliser analyses the numbers don't usually add up to 100% because those components listed is not all that is in the bag. There is usually filler - which is not mentioned by convention - which makes up the remainder.. So, an NPK of 20:20:20 is 60% listed ingredients plus 40% filler. The higher the numbers, the higher the concentration. It's not in every application that you want the strongest fertilisers, hence the varying amounts between products.