Which method is NOT effective for checking chain tension?

Observing chain length is not an effective method for checking chain tension because simply looking at the length of the chain does not provide accurate information about its tension. Tension in a chain is determined by how tightly it is pulled between two points, and a visual assessment cannot account for variations in tension that may occur due to wear, stretching, or improper installation.

In contrast, pushing and releasing the chain allows a mechanic to feel for any excess slack or tightness, which gives a direct indication of tension. Measuring with a tension gauge provides a precise measurement of the force applied to the chain, ensuring that it meets recommended specifications. Using a ruler can also provide a quantitative measure of chain slack in relation to specified tension parameters. These methods directly assess the interacting forces in the chain system, making them much more reliable for ensuring the appropriate tension than simply observing the chain's length.