Good afternoon,
There is another way to calculate the total length of multiple lines in AutoCAD without using lisp. You can accomplish this by using the command EATTEXT.
Here are the steps:
1.) It will prompt you to save a data extraction file
2.) Select the files or objects you would like to run the command on
3.) Select only the objects you want to know the total length of (Lines or Plines). You can "uncheck" all and then only select lines or plines.
4.) This is the fun part... I normally select just Length and Layer as my options. This way I can filter out lines that are on different layers.
5.) The wizard will display a table of all of the lines in the drawing, the layer they are on, and their length.
6.) Output the table to excel
7.) Open in excel and sum all of the values to get the total.