四分律行事鈔資持記 2.102

2.102

二提舍中。三十三天，在須彌頂。此墮黑繩地獄。彼天千歲，為獄一晝夜。（下皆準此。）人間數者，人間一百年，為天一日，三千年為一月，三萬六千年為一年，三十六萬年為十年，三百六十萬年為百年，三千六百萬年為千歲。（亦準大數，千萬為億，故以三千萬為三億；十萬為千，故將六百萬為六十千也。）

Second, in deśanīya: the Trāyastriṃśa Heaven is at the summit of Mount Sumeru. Here one falls into the Kālasūtra hell. One thousand celestial years of that heaven equal one day and night in that hell. (The rest below are modeled on this.) As for the count in human years: one hundred human years equal one celestial day, three thousand years equal one month, thirty-six thousand years equal one year, three hundred sixty thousand years equal ten years, three million six hundred thousand years equal one hundred years, thirty-six million years equal one thousand years. (This also follows the major numbering system, where ten million is one yi, hence thirty million becomes three yi; one hundred thousand is one "thousand", hence six million becomes sixty "thousand".)