OK first, calipers aren't that accurate. They are a decently accurate and easily accessible though. A "accurate" measurement requires a "BodPod," water tank, an Xray or an Autopsy (seriously).
The electronic scale is completely worthless and shouldn't even be looked at, except to provide amusement.
Tape tests when properly administered are fairly accurate.
HealthCentral Tape Test: 4.6%
Army Tape: 4%
Caliper Test: 5.5%
Electronic Scale: 18%, yeah worthless.
Actual is probably closer to 7% because of fat distribution. So all the tape test and caliper tests are fairly close and a good way to track your progress.
GNC has a plastic caliper for about $15, comes with directions and a chart. It's OK, but can be tricky to get repeatable results.