Norma,
In essence, I let the preferment calculator do *almost* all the heavy lifting for me. I should warn you there is a little math involved,

but it isnt too bad. Just some subtraction.

First, I figure out my total formula amounts based on my pan size, TF, hydration level, salt, yeast, residual dough in bowl, etc. Which should look something like this:
Total Formula (8x10 in pan):
Flour (100%): 196.25 g | 6.92 oz | 0.43 lbs
Water (67%): 131.49 g | 4.64 oz | 0.29 lbs
Salt (1.95%): 3.83 g | 0.13 oz | 0.01 lbs | 0.8 tsp | 0.27 tbsp
IDY (.4%): 0.79 g | 0.03 oz | 0 lbs | 0.26 tsp | 0.09 tbsp
Oil (2%): 3.93 g | 0.14 oz | 0.01 lbs | 0.87 tsp | 0.29 tbsp
Sugar (2%): 3.93 g | 0.14 oz | 0.01 lbs | 0.98 tsp | 0.33 tbsp
Total (173.35%): 340.2 g | 12 oz | 0.75 lbs | TF = 0.15
From there I create two seperate formulas under the preferment formulas box, one for the preferment and one for the soaker; all the while keeping all other variables the same. For past formulas, the recipe has been 10% preferment by total flour weight and 50% soaker by total dough weight (both formulas hydrated at 50%). So in essence, all I am doing to get the amounts is changing buttons were it says, "how would you like your preferment expressed", and changing the numbers where it says "Enter desired preferment amount". The formula for the preferment would be:
Preferment (10% of total flour weight):
Flour: 9.81 g | 0.35 oz | 0.02 lbs
Water: 9.81 g | 0.35 oz | 0.02 lbs
Total: 19.63 g | 0.69 oz | 0.04 lbs
The formula for the soaker would look like (50% of total dough weight):
Preferment:
Flour: 85.05 g | 3 oz | 0.19 lbs
Water: 85.05 g | 3 oz | 0.19 lbs
Total: 170.1 g | 6 oz | 0.38 lbs
These two formulas are the gram amounts need for my soaker and my preferement. All that is left is to calculate how much flour and water is need for my final dough.
To find how much flour and water is need in my final dough, I subtract the flour and water amounts in the preferment and soaker formulas from the total flour and water amounts which would look like this:
Flour
196.25 - 9.81 - 85.05 = 101.39g of flour in your final dough.
Water:
131.49 - 9.81 - 85.05 = 36.63g of water in your final dough.
From there, I use the total yeast, salt and oil amounts where it seems most appropriate, either in the preferment or final dough. Hope this helps.
If not, let me know and I will calculate out the pan sizes.
Jim