Know that each acre of fallow ought to support yearly two sheep at the least, then a hundred acres of fallow can support two hundred sheep, two hundred acres, four hundred sheep and so on. Robert Grosseteste
If you know how many acres you have sown of each kind of corn, inquire how much the acre the soil of that land takes for sowing, and count the number of quarters of seed, and you shall know the return of seed, and what ought to be over. Robert Grosseteste