Select the function from the drop down menu. Enter the value 'a' at which the limit to be evaluated. Move the slider or 'animation button' to find the limit value from the left side and right side. If both the value are equal, it shows the limit value. If it is not equal, the limit does not exist. If the Limit is equal to function value, then it is continuous, and the value is displayed. If it is not continuous, it shows a question mark(?).