first off, its "4.11:1", secondly, if you pull of the cover, there will be a marking... like 39/11(3.5454:1) or 39/10(3.9:1)... not sure which it is for 4.11:1, but if you devide the top number by the bottom number you get the ratio. This will be printed on the Big gear that will be poking out, just turn to find it.
or you can turn the input shaft and count how much the output shafts turn, but this will not be a very good way of getting exact ratios... ex. you have 3.54, 3.7, 3.9 and 4.11 to choose from (common ratios)