A serious question is being obscured by 'posting number crunchers'.
The point of this thread was a request for help and advice from Nicola.
Nicola, you have a Black Car - always look gorgeous when clean and a pig when dirty. I have had three black cars on the trot and I am still learning, however, I can offer the following from experience :
Before washing rinse the car using a hose pipe (not high pressure).
Using a good quality car shampoo and a pure cotton mitt wash the roof and windows, rinse these down with hose then do the front of the car, rinse off, wash back of car, rinse off, wash the sides, rinse off. No go over the complete car with the hose, use a hydra blade if you can get on with it (I have one but do not like it) then dry the car using good quality 100% cotton Terry Towelling. (babies nappies are superb)
Autoglym can be greasy, difficult to buff off, I find 'One Grand Omega Glaze' quite good, but, you must leave it on for at least 10 minutes. Buff off with cotton towelling then using a new, clean and dry towel polish. When putting on the polish do not press hard and work in straight lines running back to front working on one panel at a time. This will help to control the swirl marks, however, the above in itself is not enough.
Ideally the car could now do with a repeat shampoo and dry, I then use a Wax Polish such as Car Plan Ultra Gloss, this goes on really fast and can be polished off almost immediately again finishing with a top quality Terry Towelling Polishing Cloth. The result is a superb, deep black gloss that reflects the surroundings like a mirror. Very, very satisfying.
The next two or three polishings can be done just using the Wax Stage - you will soon see when another complete treatment is required.
When the car gets dusty spray it over with the hose and let it drain dry (or go for a short journey at reasonable speed), if shampooing again when you dry with the towel the surface looks like it has just been polished - no streaks.
The system works for me and I receive numerous comments on how well the car looks - I have had total strangers approach me to ask how I get such a degree of polish on the car.
Good luck, I hope that the above will help, Mer Polish does tend to be very electrostatic - works better on my wife's Civic Coupe than it does on mine.
regards - JonF