I'm replacing the old timber single glazed windows in my 1970s house, and whilst I am happy enough with the idea of fitting the new ones myself, what terrifies me is that I might measure up wrongly and end up with thousands of pounds worth of windows that don't fit!! In my new build it was all very easy really because I bought the windows and then built the house around them.
What's the best way to measure up- and just how accurate do I need to be?
Do I take the visible internal