Accelerometer: An accelerometer sensor is a device utilized for measuring acceleration which can be static or continuous due to the force of gravity. It can also be defined as the change in velocity per second. The accelerometer measures the linear acceleration along X, Y, and Z axes which help in telling if a component is accelerating or not. Acceleration which is measured in meter per second square (m/s2) can be used for measuring the direction in gravity. The accelerometer measures proper acceleration which is different from coordinate acceleration Although accelerometer can be used for measuring coordinate acceleration due to earth gravity where g ≈ 9.81 m/s2. The combination of two or more accelerometer can detect and measure the gradient of the gravitational field i.e. Gravity in proper acceleration. To detect proper acceleration Multiple axis accelerometer or single accelerometer can be utilized for detecting the magnitude and the vector quantity direction of the proper acceleration. The accelerometer can also be utilized detecting orientation, assist in detecting the direction in coordinate acceleration, vibration, and falling in a resistive medium, among others. The presence of a microelectromechanical system (MEMS) in smartphones allows the collection of acceleration sensors data which helps in detecting changes in position.

The accelerometer in smartphones provides the XYZ coordinate values which detect and measures the position and the acceleration of the mobile device

Note: Positive values indicate an increase in velocity, while negative values indicate a decrease in velocity, and lastly, zero values indicate constant velocity (which might not be zero).

1. Raw data from the Accelerometer sensor when Climbing down the staircase plotted using MATLAB for easy visualization.

Note: Positive values indicate an increase in velocity, while negative values indicate a decrease in velocity, and lastly, zero values indicate constant velocity. From the graph above you could see the XY coordinate starts on zero, this is because there was no movement from the subject however Z recorded some velocity. Z coordinate known as Yaw also record acceleration even though there was no movement from the subject this is because it is pointed to the sky so movement in a smartphone without been attached to a subject will spark velocity to be recorded on the Z coordinate. Also, in polar coordinate X-axis tells you how far you move from left to right while Y-axis tells you how far you move up and down. Lastly, you could see from the graph as time increases the variation also increases although from point 900 you could see there that the subject velocity reduces and later became stable this is because the subject reaches the end of the staircase and the smartphone is being removed to stop the sensors for this particular activity.

2. Raw data from Accelerometer sensor when Climbing-up the staircase plotted using MATLAB for easy visualization

Using this to contrast the climbing down graph you can see from the graph that the X and Y coordinate starts from Zero only the Z coordinate records some velocity with my explanation from the first graph the trend is obvious in this graph. Although variation is not as much as it was in the climbing down graph this is because when climbing down a staircase, we as humans our speed tends to be fast but when climbing up will move slower.

Note: acting against gravity or spark as a result of collision can also force the coordinate to record a negative value for all activities.