The accelerometer consists of a light aluminum rectangle with ball bearings at each of the four corners. One edge is mounted on a wooden block, the other is free to move. On the free end, a heavy brass weight is mounted together with a bubble level. A restoring force is supplied by a narrow V of two springs connecting the free end with the fixed end of the accelerometer. The base of the accelerometer consists of two boards which can be tipped with respect to each other. A protractor measures the angle θ between the two boards. The accelerometer can be calibrated since the acceleration will be g*sinθ if the bottom board is placed on a level surface. The validity of this calibration can be demonstrated by allowing the accelerometer to roll down an inclined plane of angle θ. In the use of the accelerometer it can be noted that, whenever the pointer on the brass block reads zero acceleration, then the bubble level also reads "level". In addition to using the accelerometer on the inclined plane, it can be placed on a rotating table about 1 meter in diameter. The table rotates slowly enough so that the accelerometer can be read while in motion. If the accelerometer is placed so that the motion of the free end is paralled to a radius, then the radial acceleration can be measured for various radii and various angular speeds of rotation. If the motion of the free end of the accelerometer is tangential it will demonstrate that, except for the initial acceleration in starting the rotation of the table, the tangential acceleration is zero. If the accelerometer is tipped before placing it on the table and the speed of rotation adjusted to show zero acceleration then the bubble level will also read level. It's interesting to compare the principle of equivalance in this situation with this analogous situation for the constant vector acceleration on an inclined plane.