Over the past months, I've been working through a tricky API design problem in the longevity project. After a number of trials, I think I've finally come up with something that does not feel kludgy, and is easy for the user to understand and use. In this post, I will describe the problem I was having, and what makes it difficult. I will show some of my solutions that didn't work so well, and finally, present the solution I've landed on. It's not perfect, and never will be, so I am eager to hear any thoughts you might have on it.