Hi all, I've been trying to develop this excel macro for mapping out a train track and locating kinks. It's been going well so far except that when the accelerometer is not exactly level with the ground, the acceleration due to gravity (9.8 m/s^2) is not only effective in the z-direction, but in the x and y as well since the whole co-ordinate system of the accelerometer is tilted. Now, I have the x-tilt and the y-tilt angles and am trying to fix this problem. Please have a look at the excel sheets I have attached. Starting from row 13 in B, C and D, I have the acceleration values in g (with 1g = 9.8m/s^w) and the tilt angles are in columns G and H. I've thought about this for a while and came up with the following formulas for acceleration. new_x_acceleration = old_x_acceleration + sin(x_tilt) new_y_acceleration = old_y_acceleration + sin(y_tilt) new_z_acceleration = sqrt (1 - (new_x_acceleration)^2 - (new_y_acceleration)^2) These seem right but when I apply these formulas (run the calibrator macro i programmed replaces the originals) the values seem very implausible. They are on the order of 10^-16 or less. Any thoughts on what I'm doing wrong?