A recipe can be based on mixing volumes of feedstocks, such as the number of bucket loads of a front-end loader, or the number of manure spreader loads. If a farmer has access to a weighing scale, then the mix can be done on a weight basis, which would provide for the most accuracy. But scales are not typically available, hence using book values, and with time, experience, should be sufficient for developing quality mixes based on volume and number of loads.