Let's see. You should by this point know how much over and over exposure your sensor can tolerate and with that information you can make two exposures to a scene while hopefully still getting a decent looking image without blown highlights or gross under exposure.

Obviously if you expose a black subject to appear grey you will get good detail in the darkest areas and if you expose to make your brightest highlight grey you will have lenty of detail in that. But that’s not the goal as you’ll have a poor quality picture either way.

The idea then is the subtly distribute the tones so that you biased the result towards shadows or highlights without too much compromise at the other end. In ‘the old days' we might bracket by half a stop to ensure a transparency that had the bias we wanted without any of the three shots actually being ‘wrong’ or useless - better to have three usable shots than one correct and two useless.

It's quite a subtle distinction but you should be able to assess which is which and why one is best and for what reason – the real point of the exercise.

A scene with snow might work!