SUM every other column - even and uneven columns

[Amapola]

We monitor the dose staff might be exposed to. There are two different values. - I have a sheet with 2 columns for each month where I input the value.

I also need to monitor the accumulated dose. Once for the last 12 months and once for all the values I have (at some stage this will be the last 5 years but I have only 2 years of data at the moment).

I'm using an array formula to caculate the first value and that seems to work:
=SUM(IF(MOD(COLUMN($H4:$CR4),2)=0,$H4:$CR4,0))
These values are in the even columns (H, J, L, N, etc.)

I have been playing around with the formula for the uneven columns but can't get that to work. Uneven seems to be more of a challenge for Excel.

In the long run, I will also need to find a formula that calculates 12 months back from the last entry. My brain doesn't even comprehend that yet. It might be easier to do in VBA? Anyway, I need to sort the issue with the uneven columns first.

Does anybody have an idea? I have cleaned up my file and could share but I don't seem to be able to attach it in this post.

Thanks, Christine

 

[ZVI]

...
I'm using an array formula to calculate the first value and that seems to work:
=SUM(IF(MOD(COLUMN($H4:$CR4),2)=0,$H4:$CR4,0))
These values are in the even columns (H, J, L, N, etc.)

I have been playing around with the formula for the uneven columns but can't get that to work.
...

Hi Christine,

Try this array formula confirmed by Ctrl-Shift-Enter:
=SUM(IF(MOD(COLUMN($H4:$CR4),2)=1,$H4:$CR4,0))

or that not array formula:
=SUMPRODUCT((MOD(COLUMN($H4:$CR4),2)=1)*$H4:$CR4)

Regards