That's true. Tests like acid or base number, viscosity changes, water, and silicon can tell a person how "old" the oil is getting. Silicon and aluminum are the most common elements in the earth's crust so aluminum can indicate dirt in the oil or metal wear. Wear metals like copper, iron, etc. can warn of a mechanical problem that may, or may not be related to lubrication. The tricky part for oil analysis while travelling is that it might be difficult to find the same oil each time it's changed. A person needs to know how the used oil compares to new oil in order to interpret the results.