Hello:

This is as old as computing, and it is not a bug. See

http://www.cpearson.com/excel/rounding.htm

for an explanation.

Pieter Vandenberg

As Pieter Vandenberg has pointed out, this is a known and natural consequence
of computers doing math in binary.  The binary approximation to 4.9
(4.90000000000000035527...) is slightly larger than the nominal value, hence
the increment used in your series is slightly smaller than you intended.

You cannot directly see this approximation in 4.9, because Excel (as
documented) will display no more than 15 figures, but you can see the full
values of binary approximations using the D2D function at
http://groups.google.com/group/microsoft.public.excel/msg/b106871cf92f8465

There are several ways to get your intended result using formulas, such as
 =ROUND(A1+0.1)
in B1, and copied across or
 =(-51+column())/10
in A1 and copied across.

The subject of this group is things that cause Excel to crash.  Your post
would have been more on topic in the general group.

Jerry