Spell size

The size of the spell in Head space is 5 times the thaums produced, thus 20 units.

You read the thaumometer:
The background magic level in this area appears to be normal.
You light the white candle.
You prepare to cast Mama Blackwing's Potent Preserver on some yarrow.
You kneel on the ground and carefully balance your candle in your hands.
Looking around to see if anyone's near, you quickly sketch some occultish-looking symbols on the floor to impress watchers and mutter under your breath.
You gently enter the mind of the frog and hold it near the candle, allowing it to dry out slightly.  You feel how uncomfortable it is, being dry.
You use the uneasiness the frog has put in your mind to harness power, and hold some yarrow above the frog, searching for moisture in it.  You point out to it how uncomfortable the frog is, and try to convince it to give up its water for the frog.
Suddenly, water trickles from some yarrow in a rush, drenching the frog, which looks much happier.
Some yarrow shrivels in your hand.
The background magic level appears to be four thaums above normal.