In the link posted by Gert, the article states the tyre manufacturers have agreed that tyres are to be manufactured to be set at standard pressures of 36/42 across all machines.
So if your 15 year old bike (my last bike was 20) has different pressures in the handbook/manual, go with 36/42, because it's about the tyre, not the bike. Unless your running the original tyres

My ZZR 1200 had 42/42 in the manual, after a service and tyre valve replacement, it rode so much better, in fact, it was the bike it should have been when I bought it.
I went back to the mechanic and we got chatting about it, I'd been setting the pressures at 42/42, and I hadn't known he set them to 36/42 , which suited the new tyres.
This is why I started this thread.......