Short positions widen the spread every other month (usually borrowing transactions that buy recent contracts and then sell forward contracts), while long positions narrow the spread every other month (usually borrowing transactions that sell recent contracts and then buy forward contracts). Both are intertemporal arbitrage.

We can briefly introduce intertemporal arbitrage.

Intertemporal arbitrage refers to an operation mode in which the same member or investor establishes the same number of trading positions in opposite directions in different contract months of the same futures product for the purpose of earning the difference, and ends the trading by hedging or delivery. Intertemporal arbitrage is one of the most commonly used hedging profit transactions.

Intertemporal arbitrage is also called "position cost arbitrage", "cross-crop annual arbitrage" or "new and old crop annual arbitrage" Generally speaking, the same futures exchange buys futures contracts in one crop year and sells futures contracts in the next crop year, taking advantage of the price difference changes of futures contracts in the same growth year. This is a common form of crop futures arbitrage trading. The crop growing year is generally bounded by August, the old crop year is before August, and the new crop year begins in September. Because of the different growth periods of different crops, the monthly division of new and old crops is often slightly different.