Uncertainty

Uncertainty refers to the inherent inaccuracy of any measurement. In science, it is important to take these margins of error into account during calculations. The act of factoring in uncertainty is known as error propagation.

Analog devices (rulers, scales, protractors) have a margin of error equal to their smallest increment of measurement, divided by two. Digital devices (electronic tools) have a margin of error equal to one of the lowest value digit.

Rules

 * When adding or subtracting two values, simply add the values together and add the uncertainties together
 * When multiplying or dividing two values, perform the operation on the values themselves first. Then, convert each individual uncertainty to a percentage of the value to which it corresponds. (The percentage is obtained by dividing the uncertainty by the measurement, and multiplying that quotient by 100). Add the percentages, or relative uncertainties, together. Take the final relative uncertainty and convert it to the number it represents in the final measurement. (Divide the final percentage by 100 and multiply it by the final measurement).
 * Apply the rules of significant digits at the end
 * The uncertainty should always be limited to one significant digit