There are a few classic measurement situations that you might face. Also sometimes you might just wrongly measure your windows by not being aware of certain things that you need to take care of. Below are different situations and their remedies:
Tiles and bricks on the same window?
This is quite possible in kitchens and bathrooms or toilets. The reason is that often you will have tiling till a certain height or splash back in the case of a kitchen.
There are two measurements for the width!! Which one do you take??
The answer is simple. Use the shortest width. If you had use the maximum width then as the blind rolls down it will not be able to continue till the bottom.
In certain situations it is possible to use the widest width. This is possible due to the fact that the actual fabric is shorter than the roll. But doing this is not advice able as it is too risky and you might waste the blind or might have to get it cut!
If you have measured the shortest width then remember that you will not be able to fit the blind's brackets on the sides cause the blind will be a little shorter. So you fit the brackets on top of the window.
Now remember that if you are fitting the blind on the outside then its always best to consider the max measurement plus a little extra to cover the complete window.
Measuring for Sliding Door / French Door
There are several ways to place blinds for example roller blinds on sliding doors meaning there can be several combinations based on the size of the door as well as the number of panels on the sliding door and also the opening of the door.
First case is with the opening of the door if for example there are two panels and the door opens on the left or the right and the panels are not too wide then just have one blind. If the panels are big have two blind. If there are three panels in the same case then have one blind covering the panel on the opening side of the door and the second blinds will cover the rest to panels. Sometimes the second solution could look a bit out of place but its very practical. The same kinda case if the the door opens on the other side. And if there are for example five panels then have one blind for the panel on the opening side and have the second one for the combination of next two panels and the third one for the last two panels.
Second senario is that the door opens in the centre. If there are four panels then you could have something like what you see in the photo. Lets say if there are six panels. In this case have one blind for the centre two panels and one each for the pairs on either sides.