When using a T or T.O.M. chart to calculate half-life, what should you do with the time (left) side?

When using a T or T.O.M. chart to calculate half-life, the appropriate action for the time (left) side is to add the half-life. This is crucial because, in a half-life calculation, you are determining how much time has elapsed as the material undergoes radioactive decay.

Each half-life represents the time it takes for half of a given amount of a radioactive substance to decay. Therefore, as you progress through successive half-lives, you need to keep a cumulative total of the elapsed time. Adding the half-life allows you to map the passage of each half-life accurately on the time scale. This addition provides a clear representation of how many half-lives have occurred and what fraction of the original substance remains over time.

In contrast, dividing, multiplying, or subtracting the half-life would not accurately reflect the cumulative time that has passed in the decay process and could misrepresent the decay state of the sample being analyzed.