In an experiment for estimating the value of focal length of converging mirror, image of an object placed at \(40 \, \text{cm}\) from the pole of the mirror is formed at distance \(120 \, \text{cm}\) from the pole of the mirror. These distances are measured with a modified scale in which there are \(20\) small divisions in \(1 \, \text{cm}\). The value of error in measurement of focal length of the mirror is \( \frac{1}{K} \, \text{cm} \). The value of \( K \) is _______.
