How to Activate Item Revision - On-Hand Availability

Hello Gurus,

I created one item, and I gave him 2 Revisions. I did 2 POs, and then I did the reception for these 2 POs.

However, when I do an Inquiry for on-hand Availability, the Revision Box is greyed out, and also they do no separate in inventory. See screen shot below.

I would like to see.

ItemA - revision X . on-hand Qty = 3

ItemA - Revision Y. on-hand Qty = 4

Let me know what Am I missing so that this box is not greyed out.

Thanks a lot

Regards

Philip