>>939474034
The numbers can be vibes-based. If you react strongly with girls romantically, it's fine to just say -1 without worrying about whether or not it's actually 0.99 or 0.8 or whatever.
If you're not sure what to assign yourself, the only solution is some form of introspection where you try to isolate your biases.

It might help to figure out if there was something else about your interaction with the guy that caught your interest. Maybe he was tall and you like tall people? Or maybe you have a preference for short hair? If enough of your interests were stimulated, it could be enough to explain some vague attraction even if sexually you're still uninterested. Knowing your preferences in many categories well enough may be helpful in separating a signal from the noise.