Selecting Every 3rd Cell In A Formula

[Craig12]

I am using the following formula, but I don't want a set of cells, I want every 3rd cell - $B$3, $B$6, $B$6, etc. How would I do this?

=IF(E2="","",IF(COUNTIF('Roster'!$B$3:B$80,E2)>-1,"",ROW()-1))

Under each day, I have a drop down list. I would like the list under the same day to not display a selection if previously used for that day. For example, if 4501A is on Monday (line 3), then on line 6 under Monday 4501A would not be available. 4501A can be available across for each day of the week, but only once per day.

Link to file:

http://www.western-transit.com/uploadphotos/Template_Sept_2013.xlsx

Roster Tab:

DropDownData Tab:

Thanks,
Craig

 

[LxQ]

I think the problem is that your dropdown list under Monday has selections of 1, 2, 3, 4, .... and your COUNTIF is looking to see if values such as 1501, 1502.. are listed in Roster!B$3:B$80

 

[AhoyNC]

This link on how to reference every 3rd value may be of some help.

https://www.youtube.com/watch?v=6cPyj8xKX84