Digital Root mistakes

Although I've finished the task (by modifying the code to suit the 'error'), I think the author made an error in the solution regarding the value of digital root.

Shouldn't digital root be only a single digit? But from the test result, the author had only find the 'digital root' from the value once.

For example if the value was 37, the REAL digital root should be 3+7 = 10 = 1+0 = 1. But the author stops the operation at 3+7 = 10.

If that was done in purpose, then perhaps he should specify it clearer in the mission description.

I'm sorry. But this is the second time the author confused me. I think the point of the mission is to find the algorithm for the right coding, and not about 'decoding' the meaning of his mission description.

How are we supposed to code the correct program if the instructions are vague/ambiguous/confusing/not clear? The basic of computer programming: "Garbage in, garbage out"!