I'm retaking PH2 and I started revising it last week and wow. Wait for PH4 and the biggest screw that is PH5. It's so easy compared to A2 lol, just make sure you know waves and lasers, particles and stars are very easy so you shouldn't drop any marks there. Just learn the lasers and the spectra and make sure you know about fibre optics and the disadvantages of multimode... That's it really.