As Ian said, get a Laser, not a Sonic.
With the laser, it projects a red dot on the point you are measuring to, so the distance is accurate.
With a Sonic, this works on a frequency somewhat similar to radar, and can bounce back from an obstacle between you and the point you are aiming for, giving you a shorter distance than it actually is.
If doing commercial work, make sure that the meter can cover longer than normal residence measurements.
Shorty.