Graduations styles come in three main categories for micrometer heads. These styles include normal graduation, reverse graduation, and bidirectional graduation. Because of this, make sure that you are aware of what type of graduation style is present on a micrometer head in order to take an accurate reading. Normal graduation style is just like the graduations seen on a standard outside micrometer where the reading will increase when the spindle is retracted into the body. Reverse graduation style is when the reading on the spindle increases as it advances outside of the body of the micrometer head. Finally, bidirectional graduation style can be used and read in either the normal or reverse style, such that it is used to make measurements in both directions feasible. On bidirectional style micrometer head graduations, the numerals for normal readings are typically in black, while the numerals for reverse readings are typically in red. Digital displays can be useful on micrometer heads no matter what type of graduations are used to improve readout precision.