One of the early questions is what the SM/CF means. If the Srating comes first in the spec it is most suited for use in SPARK ignition engines, if it is followed by a CF if higher is is suitable for SOME COMPRESSION ignition engines. The opposite is also the same, Ci/4- SH means it is suited to diesel engines and petrol engines requiring an SH rating. The higher the letter falls in the alphabet the newer the rating is. The numbers-- SAE30 = this is a mono grade and is to be used where it is called for, 10W/30 is a multi grade and means that W is a winter spec, ie it will take on the characteristics of a 10 grade when cold and a 30 grade when at operating temperature. (I am oversimplifying this) The synthetic question-- Simplified a synthertic oil is oil that is pulled apart and the equal sized molecules are arranged in such a way to make the oil more stable, and less able to be broken down. Normal oil is not as stable as synthetic and will break down sooner, Synthertic oils do have some properties that will allow them to remain stable longer under high temperatures and manage heat better. There is a lot of evidence that synthetic oil can extend oil drains but all manufactures only recomend this if accompanied by periodic oil sampling. This is not cost effective in the sump capacities in lawn and garden care. I simply would suggest it is comforting to know your oil will stand up if you do not get to servicing at the exact time required due to having a busy schedule.