Bar magnifiers are a type of magnifying glass that come in a long bar shape - We have types that are rulers and types that act as a bookmark or even a fridge magnet. They are great for reading books or large maps and can be used in many situations.
A popular model is the MagniRule which is a 30cm ruler with 2.5x magnification. This is great for people who draw a lot of people that read large construction plans or maps, simply sliding the ruler down every line when you are reading makes life much easier.
A bar magnifier is a great addition to any household and the magnetic types can be stuck on your fridge ready to use whenever you need it.