Always a pleasant experience
In this scenario, ordering a fridge freezer to go between kitchen units and a wall, with a sloping roof due to the stairs. (see left diagram)
Tried scaled images first, when that was looking too close for the various sizes (see right diagram) I resorted to maths - even broke out the trigonometry at one point before hastily realising it wasn't necessary and simple ratios/algebra were all that was needed.
Selected a fridge-freezer with a predicted 2.38 cm clearance on the top right.. and it's perfect