You can just name the variable to explain what the number is, and if you need more info, there should be a "Why?" doc somewhere explaining the context generally, WITHOUT tying itself directly to the current choice (otherwise you'll have to update the "Why?" doc every time you update the number in the code, which is almost certain to go out of sync).
No need to interweave documentation and code, in most cases. Sometimes, when we fail to write good code, sure. But let's try to write good code!
