My motion detector still reads 0.004 m after zeroing.

There is a bug in Logger Pro 3.6 and 3.6.1, when used with LabPro, where the motion detector can be zeroed, and reads zero in live readouts, but will read 0.004 m during data collection. This is enough to throw off certain energy calculations, such as the energy in simple harmonic motion lab in Physics with Vernier.

Workarounds include using a LabQuest, manually correcting the 0.004 m reading using a calculated column, or using Logger Pro 3.7 or newer.

If updating the software is not an option, follow the below procedure or used the example file to manually correct for the position error.

1) Create a calculated column, e.g. "position rezero". The equation for this correction will be "Position - 0.004".
2) Modify the definition of the Potential Energy column definition so that the variable is "position rezero" instead of "position".

Download the example Logger Pro file:
http://www.vernier.com/til/files/1914/shm_energy_corrected.cmbl