All:

I have never seen anything like this.

I have all of the following commands in the function:
Application.Volatile True
Application.Calculate
Application.Calculation = xlCalculationAutomatic

I have verified that the function will compile and that
Tools-Options-Calculation-Automatic is setup.

I have tried the code segment suggested by Mr. Ogilvy in this post and
still none of this works.

The only thing that works is to open Sheet1 and hit F9. Only then will
it calculate the function.

I spent the weekend reading/searching this group's archives. Although
I found quite a bit of interesting material, I did not find a solution.

Could this be a bug in Excel?