There should be a section of numbers labeled VDC or DC or something having to do with DC voltage. Choose the lowest number without going under the volts of the line you're measuring. The only thing the different settings do in this case is move the decimal. By choosing a lower number you get more decimal places, therefore more accuracy. On my multimeter there is 2v then it skips to 20v. So I use the 20 for measuring my lines.