The PASCO acceleration sensor is designed for use with any PASCO computer interface.  It can measure accelerations ranging up to 5g with an accuracy of 0.01g (g = acceleration of gravity, 9.8 m/s²).  The sensor produces a bipolar output that may vary from +5g to -5g, depending on the direction of acceleration.  Each acceleration sensor has two built-in features for configuring it to a particular application:

1. a tare button, used to set the output of the sensor to 0 regardless of the acceleration being applied, which allows the effect of the earth's gravitational field to be nulled;
2. a filter with two settings, "slow" or "fast", setting the frequency response of the acceleration sensor to a range suitable for the application.

The acceleration sensor is an electronic device, but a simple mechanical model illustrates its operation.  Assume a ball is suspended in a box between two identical springs as shown in the figure below.  One end of the box is marked with a + sign and the other with a - sign.

When the box is horizontal and at rest, both springs have the same length.  When the box is vertical and at rest, with the + end up, the spring connected to the + end is stretched and the spring connected to the - end is compressed.  A sensor outputs a positive voltage proportional to the amount of stretch of the spring connected to the + end.  If the box is vertical, but the - end is up, the sensor outputs a negative voltage proportional to the amount of stretch of the spring connected to the negative end. 

When the box is accelerating in a direction indicated by an arrow pointing from - to +, the spring connected to the positive end will stretch and the spring connected to the negative end will be compressed.  The sensor outputs a positive voltage, indicating positive acceleration.  When the box accelerates in the opposite direction, the sensor outputs a negative voltage, indicating negative acceleration.