Is the opposite of upside down the right side up or upside up?

Don't stack the boards upside down! Stack them ???
Thanks in advance!
It's "upside down" and "right side up."

You'd think "upside up" would be more logical, wouldn't you?
>It's "upside down" and "right side up."
Thanks, GG, I needed a refresher on this oneEmotion: smile
Students: Are you brave enough to let our tutors analyse your pronunciation?

Google also gives a modest number of hits for 'downside-up'.Emotion: smile

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If a paining is face down so they can place it in a frame they ask

Is the painting upside down or is it right side up?

Is this the best way to ask?