Coding for msg box

[Phil Hageman]

The following cells have typical values and text:

Cells Value Name
M15/M47/M79 - 110 - Chart Max
M16/M48/M80 - 100 - Target
M18/M50/M82 - 75 - UCL
M22/M54/M86 - 70 - LCL
M26/M58/M90 - 60 - Op Zero
M29/M61/M93 - 45 - Chart Min

M15 must always be greater than M16, M16>M18, etc. M47
must always be greater than M48, M48>M50, etc. Same for
the M79 cells. How do I code this (and where do I put it)
where a message comes up indicating the error? For
example: if M22 = 70, and M18 = 75, the message says
that "UCL cannot be greater than LCL", the user clicks ok,
and then fixes the error.
Would I put the code in Module1?

Thanks, Phil

 

[Phil Hageman]

A further clarification: four worksheets have this
situation.