Gnuplot in Action: Understanding Data with Graphs by Philipp K. Janert
13 Sep, 2019
A good book that describes and explains the topic well.
There's a newer revision than this one, but this is fine for my purposes and was cheap, and does a very good job of explaining gnuplot and how to use it, so I would recommend.
5V Cooling Fan for Raspberry Pi 2 3 Model B A B+ A+ ALL MODELS + 3 Heatsinks
04 Jul, 2018
Good fan for the price, very effective but a bit noisy.
Good fan, has kept my pi cool along with the heatsinks though the hot weather this summer in the UK. My pi model 1 B+ runs at 40C even when the ambient temperature is approaching 30C! Kind of noisy, but not too bad, would definitely recommend anyway because it works so well :).
It also fitted complete with heatsinks in my case after modding.