How do I step through a function evaluation in calc?

subject says it all.

You may use Function Wizard dialog to see the evaluation tree and results of each node. Use Ctrl+F2 (or its button on formula toolbar), and switch to Structure tab.

This shows the structure, but I could not see the resulting value of each node. Could you give a screenshot?

In the input line, select part of the formula and press F9.

partial evaluation