Not everybody requires the same amount of magnification, which may result in reading spectacle, either too strong or too weak. Choosing a spectacle off the shelf which allows you to read certain text size does not mean that it is the correct strength. It is important that the reading correction be balanced for both eyes and that the magnification is exact in order not to cause eyestrain that may result in accelerated deterioration.
The use of "Ready Readers" for very short periods are acceptable, as short periods of use can hardly cause harm. It is hoever still recommended to use reading glasses that are made to your exact needs which will give you the most comfortable vision when reading or working for longer periods at your desk or on your computer.