Maybe this won't help anyone but me, but when I figured it out today it was a lightbulb moment and I'll never forget how to convert mg to kg (or whatever). Here goes.
The left hand is viewed as "the big number" (kg, for instance). The right hand is viewed as "the small number" (mg, for instance). I remember this because it's kind of backwards for me as I'm right-handed. Like I said this may not make sense to anyone but me, I'm kinda wacky. Follow along...
If you wanna convert a BIG measurement
If you wanna convert a SMALL measurement
It's all in the hands, baby. Once I got the Left=Big, Right=Small thing down, I had no problem remembering which way to move the decimal.
Wah-Lah. I sat there doing metric conversions today, waving my hands around and getting 100% on my quiz. How cool is that.
I had seen various explanations of the concept, but it wasn't until I "visualized" it with my hands that it actually STUCK in my head and was useful. Previously I was always wondering "now which way was it....?"
Hope it helps! :roll