Most percentages in cheese making (that I've found, anyway) tend to be w/v rather than w/w. They are bit like "baker's percetages". In baker's percentages, you have a quantity of flour and every other ingredient is expressed as a percentage of weight of the flour. So if you have 100 grams of flour and 2% salt, it means you have 2 grams of flour.
In cheese making (most of the time), the liquid is expressed in water. So if you have 100 ml of water, it weighs 100 grams. A 30% solution of calcium chloride is 30 grams of calcium chloride in 100 ml of water. This is crucially important in salt (sodium chloride variety) calculations. If a recipe says that you have 2% salt, it means that if the cheese weighs 100 grams, that you salt with 2 grams of salt. Most brine calculations are similarly done with w/v. So if you have 100 ml of water and you want a 5% brine solution, then you want to add 5 grams of salt.
The big exception to this is Gavin Webber. For reasons unknown to me, he does his brine calculations using w/w. So while the solubility of sodium chloride is 36% w/v (36 grams of salt in 100 ml of water), it is 26% in w/w (36 grams of salt in 100 ml of water weighs a total of 136 grams and 36 / 136 = ~26%). And even more bizarrely he frequently says that his brine is "an 18% fully saturated brine solution"... which is.... frustrating ;-) But indeed, his brine is 18% w/w and is not fully saturated (which would be 26% w/w).
Even if you look at solubility tables in chemistry, they are almost always w/v, which is why I think everybody except Gavin Webber uses that system (it's much easier to calculate as well). However, there is a twist for calcium chloride. Calcium chloride makes crystals and sometimes those crystals have water set up with them. For each molecule of calcium chloride in a crystal, there can be 0, 1, 2, 4, or 6 molecules of water. This, of course changes the weight dramatically. So if you like easy math, you should by "anhydrous" calcium chloride which has crystals with no water. "Dihydrous" crystals (those with 2 molecules of water) are also common. The molar mass of CaCl2 is about 110 grams per mol. The molar mass of water is about 18 grams per mol. So each water molecule adds about 16% extra weight to the crystal. In other words "dihydrous" CaCl2 is about 1/3 heavier than the anhydrous version and so you need to add about 1/3 more to get your 30% solution (so you need about 40g per 100 ml of water instead of 30).