How is the code to the first keypad door in System Shock supposed to be found?

In System Shock, on floor 1, the first locked door with the keypad right next to it requires a three digit code, which I know to be 451 due to searching online. However, my question is, how is the player supposed to know the code using any in-game means, that is, without searching for it online?

I’ve read all the emails and logs up to that point, collected every item so far, and none provide you with the actual code or any other means to bypass the keypad. I’ve searched for walkthroughs and let’s plays, and in all of them they just input the code without actually explaining how they found it out. I’ve found some forum threads about it, but they always end up with someone just posting the code but no explanation as to how to obtain it. I’ve searched through the game manual, and it’s not there. It’s not on the box art. I’m seriously out of ideas. Am I missing something very obvious, or how were people able to get past the door back when the game first came out?