The problem is that different authors define roll yield differently, so there are inconsistencies in the curriculum. (Go ahead: prove to me that you’re surprised.)
As of the 2017 curriculum (I haven’t checked this year’s),
There is a commodities reading at Level I that defines roll yield as the difference between the spot price and a futures price, or the difference between two futures prices with different expirations.
There is a commodities reading at Level II that defines roll return by comparing the prices of two futures contracts: the near-term futures price minus the farther-term futures price. It further divides this difference by the near-term futures price to get the roll return as a percentage.
There is a currency management reading at Level III that defines roll yield as the (absolute value of) the difference between the spot price and a futures price, that difference being divided by the spot price to get the roll return as a percentage.
There is a commodities reading at Level III that defines roll yield as I have done here: the difference between the forward premium on the new contract and the forward premium on the old contract when the old contract expires and is rolled over to the new contract.
The short answer is that Finquiz’ formula is, in fact, correct, and the one that _ you know _ is, in fact, wrong; however, each appears in the curriculum, so it’s not entirely your fault.
Only if you want to earn all of the points on that question.
I just received from a candidate her answers to the morning session from the 2017 exam (the real exam) which I’ll be grading for her. Question 1A asks you to calculate a collateral return and a roll return.