Once you have downloaded the appropriate version of the calculator spreadsheet, 
you may rename it anything you wish, and file it in any convenient place in 
your filesystem.

The spreadsheet file contains three separate sheets. The "Basic" (blank) sheet 
is ready to use as a feed calculator. The light yellow cells are for data 
entry--that is, the weights of the various ingredients you are considering 
using in a particular mix--and the light green cells contain the formulas 
that will recalculate protein amounts and percentages, amounts of ingredients 
in a 25-lb batch, etc. (Click on one of the green cells, and you will see the 
formula it contains in the formula bar up top.) Of course, the colored backgrounds 
are illustrative only--you can re-format those cells to have no background color 
if you wish.

The other two sheets ("Winter" and "Starter") are examples of the sorts of feed 
mixes you might generate, using this electronic spreadsheet. On these sheets, 
actual values have been entered for the ingredients, and you can see the results 
(one a mix for layers in the winter house, and another for chicks on pasture).

Now that you've seen how the spreadsheet works in practice, go back to the 
"Basic" sheet.  Update the spreadsheet to reflect the actual ingredients you 
will be using. For example, suppose instead of alfalfa meal you are using 
sunflower meal. Simply replace "Alfalfa meal (.17)" in Cell A12 with 
"Sunflower meal (.35)." Then go to Cell C12, the formula for calculating the 
amount of protein in the weight of ingredient in Cell B12, and change the 
formula to reflect the changed percent protein. That is, change the formula 
from =B12*0.17 (alfalfa meal is 17 percent protein) to =B12*0.35 (sunflower meal 
is 35 percent protein). After updating your ingredients list, you might want to 
duplicate the new blank sheet several times, renaming each copy for a mix that 
you wish to experiment with.

After you have modified the spreadsheet to reflect your own available ingredients, 
you are ready to plug in values (weights) to hit a target protein percentage. 
Please note, however, that for the percent protein of the mix (Cell C18) to be 
correct, the total weight in Cell B18 must be 100 pounds.

Once you have become comfortable using the spreadsheet as designed to formulate 
feed mixes, you can modify it any way you wish. For example, you can easily add 
columns for calculating amounts and percentages of fats and carbohydrates, or 
the total cost of feeds your are considering, using the existing columns and 
their formulas as examples. See your spreadsheet program's manual or Help section 
for assistance.