The £1 a window seemed to be the aim when I started five years ago, not sure that was really in effect 15 years ago, anyway £1 is a bit of a barrier, it's a nice round figure, easy to calculate and a house with 8 windows is not overly expensive to the customer.
What I tend to do now is view the property and location of windows while still using the number of windows as a reference point. Then price accordingly, with refining cleaning techniques, getting more customers in an area and staff it now takes less time to clean a house than it did 2 to 3 years ago.
So, a simple access semi will work out at the magic £ while a similar house with access issues for a reach over an extension would be more, all prices + 30 to 50% if wanting 8 wky rather than 4 wky.
We now have tracking on the vans and the van has to hit an average hourly rate inc travelling times.
This has been very revealing in the argument of 1 man 1 van or 2 men 1 van - now all the guys go out singly !
So in short, it's not just an x amount for a window...! I get around 70% of everything I go and quote, usually get 0% if forced to give price over phone or leave a quote through the door
Darran