Mathisfun.com bills this as a Least Squared Error calculator , but I don't think it is a calculator. I think it is a nice visual aid that demonstrates how the regression line/equation change as your data changes. The static photo below doesn't do this interactive website justice. You can drag and drop any of the dots on the scatter plot and watch as the regression line and regression line equation are recalculated to best predict Y based on X. It doesn't explicitly show the math going on behind the scenes, but it is a nice compliment to your LSE lecture. https://www.mathsisfun.com/data/least-squares-calculator.html

When I teach regression, I usually introduce the regression line by reminding my students of the long-ago days of algebra class and graph paper and rulers. MathIsFun.com has created an interactive applet that mimics the graph paper and allows users to adjust the y-intercept and the slope . This is a slightly fancier, more high-tech way to get your students thinking about the linear equation and then fitting that old knowledge into the new concept of regression. Use the bars to adjust slope and y-intercept as a quick linear equation primer before teaching regression