Calcium Chloride

I recently bought some cheepo CaCl2 from SSS and it said on the tub "Calcium Chloride 77.5%" . I asked the supplier what the other 22.5% was but they said it didn't refer to the purity but to "the assay of calcium in the chemical makeup" I am still none the wiser because that sounds as if it would mean the percentage mass of calcium in the molecules, which I think would be less than 40% and why would I want to know that anyway?
Can someone enlighten me?
Thank you
Anhydrous or not?

I suspect that it is what is colloquially known as technical grade, which seems to be anything from the state it was dug out of the ground/came out of the initial process to a product that has had some contaminants removed but is still not close to "pure". It's one of the reasons I have moved to industrial suppliers for chemicals. They have may have nebulous names for the varying grades of chemicals they supply but each grade will have published specifications so you can make a judgement on what is best suited for your use. There is, of course, a premium to pay for the known quality so I try to get around that by bulk-buying the common chemicals on about a five year rota. So far, it seems to have worked.
Thanks Mike
It's supposed to be anhydrous, so I thought that perhaps it was just some hydrated in there. I'm not bovvered about purity as long as there's nothing alarming in it, in as much as the kids only use it for an example of exothermic heat of solution: semi quantitative at best. I just wanted to check that the other 20 odd percent wasn't going to do something funny. However, I was more confused by the supplier's answer to my question. That is a direct quote of what they told me and I don't understand it!