NYC has three basic long standing rules when it comes to pocket knives:

1. It can't lock open. (they seem to interpret the law as, any knife that locks open is a potential gravity knife)

2. It can't be longer than 4"

3. It can't be carried in the open (that means, no blades clipped to your pocket for example).

Of course, there are certain exceptions to these, but that is the general ruling on knives.

The whole gravity knife statute is, IMO, an outdated and vague law that should be modernized and clarified. One has to remember that, when it was written, one-handed opening blades weren't as common as they are now. For the most part, they've entirely replaced the traditional pen knife in American society.

See, at the time, you either had people carrying traditional pen knives for day to day activities or people carrying switch blades, gravity knives, daggers, ect so they could get them out fast in a fight; with little in between. The law was originally written to prevent the latter without taking into account changes in technology and public opinion over time. They never could have foreseen the advances in technology that went into something so simple as a pocket knife.

It would be like me trying to write a law about computers based on 1970's technology. At that point in time I couldn't have even imagined how ubiquitous and advanced computers have become. Things that are taken for granted today (like the internet) weren't even imaginable back then.