  This paper aims to identify three electrical systems: a series RLC circuit, a
motor/generator coupled system, and the Duffing-Ueda oscillator. In order to
obtain the system's models was used the error reduction ratio and the Akaike
information criterion. Our approach to handle the numerical errors was the
interval arithmetic by means of the resolution of the least squares estimation.
The routines was implemented in Intlab, a Matlab toolbox devoted to arithmetic
interval. Finally, the interval RMSE was calculated to verify the quality of
the obtained models. The applied methodology was satisfactory, since the
obtained intervals encompass the system's data and allow to demonstrate how the
numerical errors affect the answers.
