Whats the difference int he tow percentage back from player sale?

I'm a little confused to what an earth is the difference between the two options of percentage from next sale when selling a player.

Can someone clear this up for me please.

As fair as i know say a 50% of next sale, if you sell your player with it, if they sell him on for say 10 mill? you get 5 mill?

Then percentage of profit say you put 50%, they sell him for 10 mill, if you sold him to then for 5 mill, you would get 50% of the 5 mil profit they made, you would get 2.5 mill??

Is that right?

One is a percentage of the full resale value, the other is a percentage of the resale profit.

Example: I sell Super-Striker to Tottenham for £10m, who a couple of seasons later sell him to Barcelona for £30m.

A: With a 10% of next sale clause, Tottenham will have to pay me another £3m (10% of the £30m they sold him for).

B: With a 10% of profit on next sale, Tottenham will only have to pay me another £2m (10% of the £20m profit they made on the deal).