Small nitpick, half a decade late: bottlecaps are arguably proportional controllers—the pressure they exert on the inside is proportional to the pressure applied by the inside, until the bottlecap hits a performance limit and breaks.
Small nitpick, half a decade late: bottlecaps are arguably proportional controllers—the pressure they exert on the inside is proportional to the pressure applied by the inside, until the bottlecap hits a performance limit and breaks.