How are tactics rating points given?

I've been having massive (+/- 100 points) fluctuations in my tactics rating. I've noticed that sometimes I get a lot of points for super easy tactics, and other times I get 1 point for a super hard tactic I took too long on.

It seems the consensus on the forum is 

1. You get more points for solving hard problems above your rating

2. You get less points for solving easy problems below your rating

If you take too long on either of them your points go down.

looking at some of the big wins (+13) I've gotten right, I don't see how many of them are considered "hard" tactics. Some of them are even simple mate in 1 tactics that just happen to be higher rated. 

Are tactical ratings for problems assigned based on the source game? Or are they assigned based on how easily people get it right? It's pretty annoying to have giant point swings after a bunch of +1s.

I'm not 100% sure this is accurate anymore but the way tactics used to be rated was based on treating them like a player. They would get assigned an initial rating and if someone got it right, the rating would drop as if the tactic has lost to a player with that tactic rating. Same was true for a wrong tactic. So the ratings fluctuated based on that.

I think that is still true.

As to scoring you get:

https://www.chess.com/blog/News/chess-com-dev-update-april-28-2017

and

https://www.chess.com/blog/News/chess-com-dev-update-may-26-2017

There have been some additional updates for sure that deal with the tactic selection algorithm, though I don't know if there have been other structural changes. Early on (after the April 28th update) the algorithm made it really easy to get a high rating, it was tweaked and then it caused some deflated ratings and last I tracked it, I was getting about 60% of the tactics higher rated than my current rating.

Interesting, I'll read some more into this. Thank you for your reply.

That is correct. Successfully completing a tactic will give at least 1 point.

 I don't know of any other topic than the tactics board and puzzles that generates as much discussion. As already pointed out (is that a pun?), points are awarded or deducted based on relative rating of player/puzzle and time to solve. And as wb noted above, if you take forever to solve a puzzle but get it right, you won't lose any points; of course, you likely won't earn any - but I've come to appreciate that trying to not lose a lot of points is better than only getting a few. Still, I mess up more often than I care to. 

Martin, thanks for the links; very helpful in other areas, too.