To calculate the total length of multiple lines click on the lines and enter DATAEXTRACTION. A pop-up window appears. Now select create new data extraction and choose next. Type in a new file name and click save. Select the lines in your drawing and click next. In category uncheck all except geometry and length. Change the output data to Xls and choose the excel file. And it will be saved in the excel file. Lastly, open that excel file n add all the lengths.