Thanks both for replying to this thread - have fixed the problem in a
'better' way - I did a quick search on the web and issues with FP maths is
more fundamental than I previously understood; rounding to 15dp IS a viable
solution.

Thanks again.

"Rick Rothstein (MVP - VB)" wrote:

Am having problems with the use of trig functions within in VBA.

sin(worksheetfunction.pi/2) = 1 //this is ok
cos(worksheetfunction.pi/2) = 6.12303176911189E-17 //this is causing me a
real headache... it should and needs to equal 0.

For reasons I wont go into I cannot fudge with the round() function.

I have tried using decimal type to define PI, but have not succeeded (not
sure that I am coding correctly, but VB 'truncates' anything over 15 sig.
figures in the programming environment, so I can't increase accuracy by
simple const definition.

I don't think there is anything you can do about this (except to use some
kind of rounding operation)... these slight and minor discrepencies with
floating point numbers is a well-known problem... it is inherent in the
system used to store them. If this is new ground for you, perhaps these
links will help...

INFO: Visual Basic and Arithmetic Precision
http://support.microsoft.com/default...NoWebContent=1

(Complete) Tutorial to Understand IEEE Floating-Point Errors
http://support.microsoft.com/default...NoWebContent=1

Just out of curiosity, why are you opposed to using the Round function with,
say, 15 for the number of decimal places?

Rick