An accelerometer is an instrument that measures the sensible acceleration along its sensitive axis. This sensible acceleration is the ratio of the sum of all non-gravitational forces acting on the accelerometer, along its sensitive axis, to the mass of the accelerometer.

It is a common misconception that an accelerometer can measure acceleration due to gravity. If that were true, then a missile's navigational computer would not have to calculate this acceleration as a function of the missile's position in the gravity field.

When an accelerometer is placed on a table, with its sensitive axis along the plumb line, it will measure approximately 1 g of acceleration. However, this is the "acceleration" caused by the force of the table on the accelerometer, a force that balances the force of gravity to keep the accelerometer stationary.

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