# Propagation of error in sum and multiplication

- Author:
- Simona Riva

- Topic:
- Multiplication

An experimental measurement is always affected by uncertainty (error), that may depend on the method used to measure, or on the instrument's precision, etc.
This example illustrates the propagation of error when we sum or multiply the lengths of two objects

*a*,*b*. Enter the*mean value*and the*absolute error*of each length in the related input fields, then select the operation to view. Move the sliders to explore the range of each length and observe how the sum and multiplication are affected. Click the button to reset the lengths to their exact measure (i.e. error=0). The unit of measurement has been intentionally omitted - a formally correct way to write a measurement is