Finding the Min Positive Value of Dynamic Data

Can't you set your template up such that B1 initially contains a value less than any number you would be expecting? It will be replaced therefore on the first upload of data. And in B2, a value greater than any value you would be expecting?

how do I assign a value to the cell without it replacing the formula?

I think its my fault for the way I posed the question orignally when I said "So I've tried the obvious attempt in B1, =max(a1,b1) which will only work if my Net P/L is positive. But if my P/L is negative it will remain zero, since that was the default value of B1 before calculations begin." Maybe that was not the most precise way of describing it. Cell A1 has the streaming data coming in from DDE link, B1 contains =if(b1>a1,b1,a1) and that is all B1 contains, so I guess the formula recognizes no pre-assigned value for B1 other than its circular reference formula, and so it always returns 0 by default, when A1 is less than 0. But on days when I start losing money right off the bat, it would be helpful to know at what point I was losing the least amount of money.

Does B1 = 0 or "" initially? Can you change your formula to

=if(b1="",a1,IF(b1>a1,b1,a1))