What is IT?
Is there a letter prefix to the serial number?
If the revolver is not marked as to model (under the crane where the cyl swings out) it is what is called a "pre" model 42, probably made prior to about 1961 or so... and it is more valuable.
Because this revolver has a flat cyl release it is probably an earlier gun, (though some airweights continued to have flat releases a lot longer.) I don't have my references at hand, so can't set a year with any accurace.
Under the grip, near the back end of the frame there should be a pin that can be used to lock the grip safety... these are often missing...but if present adds to value. Likewise a box/papers/accessories also increase the value of the gun.
From the pic I can't tell the exact condition of the gun, but as it stands I would price it $300-350 depending on condition... add the other items discussed and get in the 95% condition range and you will get the gun up into the $500 area.
V/r
Chuck