You might just naturally assume that all your falls are flat surfaces, but there’s a chance that they slope slightly. When that’s the case, you can find yourself halfway through hanging your wallpaper before you realise it’s not as straight as you first thought. Don’t worry, it’s perfectly normal and there’s a simple solution. You can see how true your walls are before you get started by drawing a guideline with a spirit level. It may end up leaving space at the top and bottom of your wallpaper, but you can just paint an inch-wide white strip to hide any ends that don’t quite match up.