Start with a whole town on the screen. Every click zooms in ×10. Stop at each landmark, answer the note, and count the clicks.
Grams and litres zoom the same way. Split into 10, look at one piece, and do it again. Three zooms take you from kilo to plain, or from plain to milli.
Six trades. Use the zoom in your head: one step is ×10, kilo to plain is three steps.