BT subnet mask

[loltim]

Hi, just setting up a router for a mate, we've got a static IP and a subnet mask of 255.255.255.254.

When I try and enter the subnet mask I have two choices. 255.255.255.240 and 255.255.255.248. Can I enter a custom subnet on the home hub?

 

[loltim]

Just found this:
If you have purchased 5 public network static IP addresses then your subnet mask will be 255.255.255.248.
If you have purchased 13 public network static IP addresses then your subnet mask will be 255.255.255.240.

what if I only bought one IP address?

 

[loltim]

OK just rebooted the router (after purchasing static IP) and it's picked up the given static IP.

But, static IP is still set to disabled on the home hub. Does this matter? It's BT infinity btw.