On the Subject of Digital Root

Okay, root of 64? - 8. No, the other kind of root. 4 then! NO, THE OTHER KIND!

• On the module there are three numbers in a row, another number below them, and buttons with the labels yes and no.
• Determine if the lower number is the digital root of the three upper numbers.
• A digital root is determined by adding the three numbers together, then taking each of the digits of the answer and adding them together. Continue doing this until you are left with a single number.
• If the lower number is the digital root of the three upper numbers, press the yes button. If it is not, press the no button.