We get these sorts of readings either due to wiring errors wiring loads in series that divides up the voltage.
THIS OFTEN HAPPENS WHEN WE MISTAKINGLY WIRE INTO A SWITCH LOOP--up in the attic ------- where the white is NOT a neutrall!!
Or what is called phantom or ghost voltages that is really no useful voltage at all,and is isiully from using digital meters AND THE CIRCUIT IS open .
This is the only type tester that is acceptable for solid circuit testing.http://www.mytoolstore.com/klein/69115.html
It is a SOLENOID type tester and is made by several companies.
Digital and analog meters are really for electronic projects and low voltage trouble shooting .
120v and 240v are "LINE VOLTAGES"