I inherited an Inventory Spreadsheet that calculates min/max levels and is used for Forecasting. However, I'm not sure what the some of the columns are calculating. Unfortunately, I'm no excel guru - in fact I'm a beginner and I'm taking classes. Therefore I've attched a copy of the spreadsheet for review in hopes that someone can explain to me what my predecessor was calculating. The formulas arer there, I just need to explain how things are being determined. Thank you in advance!

Or if someone has a better Forecasting Inventory Spreadsheet that would be great as well.

USG - stands for usage I assume
Columns I need explained a
M (Usg% Inc/Dec) what is being calculated in the formula
=IF((F2=0),((((H2*12)/I2)-F2)/1),(((H2*2)-F2)/F2))
N (New Inv Min) how and what is being calculated to come up with this #
=SUM((((K2/365)*12)*J2))*L2
O (New Inv Max) how and what is being calculated to come up with this #
=ROUNDUP(((N2*2)+0.1),0)