In reply to doc_h:
I've seen a lot of variation in grades between walls. Even more pronounced is the variation between routes inside and out - with, grades also differing between areas outside.
Part of this, I'm sure, is that individual climbers have different strengths and weaknesses, and different styles. Likewise routesetters. Also, you get used to certain kinds of hold and move. E.g. climbing somewhere where they've grippy paint on their boards, or features, versus somewhere with smooth plywood; similarly, moving from limestone to grit, or doing a "very trad" chimney from the early C20, originally done in big boots, versus a face climb established in the 1990s. I'm also used to a fairly clean gym; when I go to an indoor wall that's filthy, and the crimps are covered in black slime, that makes a difference - though I try to think of it as training for green grit and greasy rock .
I think sometimes you need to acclimatise, and you tend to learn something when you meet with these disparities. But, I think the best thing is to get to a point where you can set your own aims and challenges, understanding the route and your abilities and weaknesses (which does not = height), and being content with a good climb, even if it's "a grade lower" than "what you usually climb". Conversely, the worst thing is blaming the routesetter, who, despite their mountain of qualifications, is often being paid minimum wage to take our whining in between kiddies parties...
Also, it all becomes irrelevant when you get outside and realise that there's no way you're going to turn a heelhook into a high rockover, on a matched crimp, well above your last piece of gear/boulder mat. Whatever you can do inside, climbing outside's pretty mental (in one sense or another).
My 2c.
Post edited at 14:25