Query about MC34063A calculations

[FvM]

This is so annoying.

It's been said...

the voltage across the diode drops slowly from 12V to below 1V over the course of several seconds.

The "voltage across the diode" is assumed to be a pulse waveform, so I really don't know what the words mean to say. And what's the voltage sign? If you are observing 12 V forward voltage, you may want to check the diode, your instrument, or both.

My bread board basic boost converter works beautifully and outputs a steady 18V.

Where as with the bread board circuit the voltage across the diode is pretty much instantaneously below 1V.

Both statements don't go well together, I think. If there's 18 V output voltage, how can the diode voltage show "below 1V"