Why the arithmetic is open

A birth chart begins as a calculation. You feed in a date, a time and a place, and a program works out where the sun, moon and planets were. The essay asks a simple question about that step: can anybody outside the company check it?

It opens on the promise itself: every chart the company prints will show the arithmetic behind it, starting with which of the four Lahiri settings produced it. Then it hands you a check you can run today. One of the blog's other writers has published the four steps that turn a calendar date into a running count of days, the number every astronomy program starts from. Do the steps with a pencil. Then look up the same date on Horizons, a free public service run by NASA's Jet Propulsion Laboratory. If the two numbers agree, the essay was right. If they disagree, you can prove it, and nobody has to take your word for it. Complaining requires people to think you are worth listening to. Reproducing does not.

Three things have to be printed on a chart before it can be checked that way. First, the source of the planet positions, named with its version number, because those files get rebuilt and the numbers change slightly when they do. Second, the exact setting used for the ayanamsha, one of the choices a program must make before it can produce an Indian-style chart. Third, the working, wherever the working is arithmetic a person could redo.

Then the harder half. When nobody outside can repeat a calculation, a mistake in it stops looking like a mistake and starts looking like a different tradition, so it can sit there for years with nobody at fault. And there is nothing except the operator's own conscience standing between calculating a number and simply choosing one. The essay is careful here: it accuses no company of doing this, only of being impossible to check.

Being checkable costs something, and the essay lists the costs. You cannot upgrade your software quietly. You have to answer corrections from strangers, including the wrong ones. You lose the excuse of a private engine. And one common library is free only if you publish your own code in return.