Trends

[Newbe0n]

Does anybody know the maths behind the trend formula in Excel, I am needing to predict a expiry date based on the ware and tear of a part, but can't find a formula to do this. The excel trend function seems to be exactly what I'm after but I don't want to use an Excel plug in for my app. And besides it is always nice to know how these things work!

[manuelromero]

the function used by Excel it's Square Least Method (o minimos cuadrados, in spanish) and any statistic book like linear regression

the equation is Y=A+B*X

where
B=(n*Sum(X*Y)-Sum(X)*Sum(Y))/(n*Sum(X^2)-(Sum(X))^2)
A, is obtain solving the equation
A=(Yaverage-B*Xaverage)

and
n, the number of data
X, Y, the points

i hope you understand me

[manuelromero]

Also look in the Excel help for SLOPE function

[Newbe0n]

That'll do nicely Sir!

It's at this point I wish I had paid more attention in maths!! Thanks for the answer, after a short pondering I now understand it.

[dinosaur_uk]

Just in case anyway was too lazy to code it up...

i have uploaded a sample...

[yrwyddfa]

http://www.vbforums.com/showthread.php?t=311225