scenario possibly need conditional formatting or pop up

[lezawang]

Hi I have scenario like the following: I do not want to allow 2 material to have same week (to be borrowed same week). I want to give a user an message saying he can not have that week because other device reserved that week.
For example Device 10 is taken in week 4 then later device 200 is also taken in week4. That is not allow. I want to excel either highlight device 200 raw or give a pop up saying not allow. Same apply on device 150 which is taken in week 10 then
excel should not allow device 66 to have same week. Thank you so much.
[TABLE="class: grid, width: 100"]
<tbody>[TR]
[TD]device#[/TD]
[TD]week[/TD]
[/TR]
[TR]
[TD]10
[/TD]
[TD]4[/TD]
[/TR]
[TR]
[TD]40[/TD]
[TD]1[/TD]
[/TR]
[TR]
[TD]100[/TD]
[TD]2[/TD]
[/TR]
[TR]
[TD]200[/TD]
[TD]4[/TD]
[/TR]
[TR]
[TD]150[/TD]
[TD]10[/TD]
[/TR]
[TR]
[TD]170[/TD]
[TD]40[/TD]
[/TR]
[TR]
[TD]66[/TD]
[TD]10[/TD]
[/TR]
</tbody>[/TABLE]

 

[Fluff]

Assuming that your data starts in A1.
Select A2:B to end > Home tab > Conditional Formatting > New Rule > use a formula > =COUNTIF($B$2:$B2,$B2)>1 > select format > OK

 

[lezawang]

Can you kindly explain what this formula does? I mean I do not understand countif arguments? thank you once again

 

[Fluff]

There are plenty of sites on the web that explain what the functions are & how to use them.
Try searching Excel Countif