The "Proportion Calculator" is the first tool in the "mbar School Tools" series. This App calculates proportions (direct or indirect), also known as "rule of three" by entering three known values and hitting "Calculate". The App will calculate the missing value for you! NEW in Version 2.0: The formula used for calculation can be shown with all details after a calculation has been made! You can use this feature to increase your understanding in solving the rule-of-three. A history of calculat