For almost all units of measurement Text Control uses twips. Twip is a fabricated word meaning twentieth of a point. A point which is a unit of measurement for type, is approximately 1/72 inch but often assumed in graphics systems sach as Windows GDI to be exactly 1/72 inch. A twip is 1/20 point and hence 1/1440 inch.
Type size is expressed in units called points. A point is very close to 1/72 inch, so close that it is often defined as exactly 1/72 inch. The point size indicates the height of the characters. For instance, when we speak of 12-point type, we are referring to characters that are 12/72 inch high from the top of the ascenders to the bottom of the descenders.