Looking to add 4 GB RAM to my partner's HP ProBook 4535s.
It supports PC3-10600 (1333 MHz) and PC3-12800 (1600 MHz), according to the Crucial System Scanner.
The least I can spend on the 4 GB module, the better.
I've found the following module from Ebuyer: Crucial 4GB DDR3 1333MT/s Laptop Memory for Mac (£24.52 after delivery costs)
I'm sure that is just the name of the product on the website, and that it'll work in the HP laptop just fine, but it's best just to make sure.