HP80 TVM sequence?

[Dave Britten]

There are a few interesting details about the HP 80's operation that will perhaps give you a better understanding of how it works:

There are no TVM registers. All computations are performed directly on stack values. (This goes for statistics operations as well!)

Because of this, the TVM keys simply set internal flags corresponding to each variable and enable stack lift to prepare for the next input.

When computing a result, the calculator checks which TVM key flags have been set to choose which equation it needs to use, and then gets the inputs for that equation from the stack registers.

So only two things really matter here: you've put the values onto the stack in the correct order for the equation (usually left-to-right when looking at the TVM keys), and you've pressed the right TVM keys to turn on the internal flags to select that equation, but the order doesn't matter for this. So as long as you're entering the values in the correct left-to-right order, you can press the TVM keys in whichever order you wish (with the exception of the final selection of the variable to solve for at the end) and still get the correct result. Why you would really want to do this is anybody's guess, but you can.