If you are specifying a length in L a T e X , but do not specify the appropriate units, you will generate the error below:. I'll assume that you meant to say pt, for printer's points. To recover gracefully from this error, it's best to delete the erroneous units; e. See Chapter 27 of The TeXbook. See here to learn more about lengths in L a T e X.
First, we introduce the LaTeX measurement units. All LaTeX units are two-letter abbreviations. You can choose from a variety of units. Here are the most common ones. The point is the default unit and 1pt is the default length.