A d-pi is easy. It's a marble.
Okay, if you want to have an easier time of telling what number is rolled, paint a stripe around its midsection and tick off distances equal to its diameter along it. When it stops, choose the distance at its highest point. It's perfectly fair.
Okay, if you don't want to have to deal in irrational analog numbers... sorry, dude, it's pi.
But, gosh, the d30 is so annoying to me... it's been around for decades, and back in the day, everyone swore by them and never, ever used them. They'd claim they'd roll days on a calendar, but... nope, they never actually did that, just thought they might.