Hi

I have used used data manipulation in Excel to use 1 month's worth of river data to work out what it would be over a year by the use of another rivers data. The following steps were taken:

STEP 1
I plotted 1 graph that gave me a relationship between 2 primary variables, then used the equation of this line [Equation 1] to work out a set of values, X.

STEP 2
I then plotted another graph showing the relationship between a new primary variable and the X values, then used the equation of this line [Equation 2] to work out another set of values, Y.

My outcome involved me plotting my Y data against days of the year for the river. I want to know what my confidence interval would be given that the Y data I used is not primary. It is the result of an error from using 2 estimations from Equation 1 and 2.

I have both R^2 values for the equations of these steps, but do not know how I can use this information. I want to be able to plot an upper and lower boundary limit on my final graph, and would need to account for both these errors. If anyone could help me I would be forever grateful

Many thanks,

Richard