- Those slot machines in a legit physical casino are being periodically calibrated and following regular maintenance.

-Those slots in a legal online gambling platform that are either handled by the site itself or a game provider, are also following legal measurements to ensure that they follow the stated algorithm.

Transparent in terms of what? Fairness? There's no way a gambler can find the legality of it. On that, just trust the reputation. And besides, most gamblers doesn't really care about transparency, fairness or everything along those lines when they are gambling.