First of all, you have impeccable taste in blades. The Calypso is a wonderful knife.
Now, technically, I'm pretty sure that it's a number one philips. One size up from a jeweler's screwdriver.
I just used one of those promotional screwdrivers that has a clip on it to put on your shirt pocket. Although, come to think of it, I've also used my Leatherman Micra. And my keychain SAK. And my Microtechnician. And...