Suppose column A contains a list of dates.

A1 is July 21, 2008
A2 is July 22, 2008
A3 is July 23, 2008

And so on. The dates in column A are determined by a formula, so they
will change from day to day.

Suppose column B contains a list of daily prices.

B1 is $80
B2 is $90
B3 is $100

And so on. The prices in column B are determined by a formula, so
they will change from day to day.

Suppose column C contains a formula that calculates the data in column
B. The first time that formula in column C finds a cell in column B
that exceeds $100, I want it to update cell D1 to contain the date in
column A.

So the formula looks at B1, does a calculation, but is content.
The formula looks at B2, does a calculation, but is content.
The formula looks at B3 and "sees" that B3 exceeds $100 so the formula
tells D1 to inherit the date of A3.

Does that make sense?

I know I can go to cell D1 and type "=A3" but that's not the point.
The cell that contains the correct date may be A4 tomorrow, and A10
the following day. So hard coding D1 to A3 will not work for this
purpose.

I want the formula in column C to "push" the date to D1.