A pressure gauge, in general, is meant to measure that current condition of the liquid or gas that it is measuring. The differential pressure gauges are meant to measure different things. For this type of pressure gauge, you can use this when you want to know how much pressure you are applying to the brakes. There are some pressure gauges that are still analog and some people prefer that because they are used to it.
Those who would like to get immediate and accurate readings would rather choose digital pressure gauges. There are some pressure gauges that will display the measurement all the time. All that people have to do is to check to get the reading that they need.