Building Automated Trading System

I am trying to create an automated trading
system in Excel. I need to get Excel to return
a specific value if there is a change in the
value of another column. And then another value
for the cell immediately after has to return
another value.

Ex. Cell K93 is “-“. When K94 changes to “+”,
N96 has one formula, and N97 has another. Then
all of Col N has this second formula until Col
K changes to “-” again in say, K423. Where N425
then has one formula and N426 has another
formula. This formula in Col N continues until
Col K changes to “+” again, and this repeats to
the end of the data.

Any help would be greatly appreciated. Thanks.