Palaeography or paleography is the study of historic writing systems and how to decipher and date historical manuscripts and handwriting. The shapes of letters have changed over the centuries, often to reflect the tools and materials used to write them and methods of teaching. Writing used to be time consuming, and paper and parchment were expensive so authors used many abbreviations and ligatures [joining two letters together into a single form] to save effort and space.
Until the twentieth century many people learned to write in a specific style that was fashionable so there tends to be a uniformity which makes it easier to read documents written by different people once you have learned the basic letter shapes. Some documents, such as wills, tend to be formulaic: Standard simple phrases are used and the documents are written in a certain order which can make them easier to read and interpret.