If you own multiple two-cycle yard machines, you probably have at least three gas cans in your garage—each with a different gas/oil mixture. A single-mix oil eliminates the need for multiple gas cans and frees you from ever performing a gas/oil ratio calculation again.
A single-mix oil works with all gas/oil ratios, from 16:1 to 100:1. Just add a packet to 1 gallon of gas and use it on any two-cycle engine. The product contains a fuel stabilizer, so you can just store your equipment at the end of the season without adding anything else to the gas tank. It's available at most small-engine dealers or online (search “single mix oil for 2-cycle engines”; one brand is opti2-4).