Field of the Invention
The invention relates to a sight, and more particularly to a sight capable of being zeroed quickly by an impact-point regulating mechanism. 
Description of the Related Art
Referring to FIGS.  1 to 3, a zeroing method for an impact-point regulating mechanism of a sight is shown.  Referring to FIGS.  1 and 2, a regulating cover 10 is pulled up to become unlocked and afterwards is rotated to align a zero point of the regulating cover 10 with a zero point of a scale ring 20, whereby the impact-point regulating mechanism is zeroed.  When the impact-point regulating mechanism is zeroed, the regulating cover 10 is released and returns to a locked state as shown in FIG.  3, whereby regulation of the sight for impact point can be performed. 
FIGS.  4, 5 and 6 depict a cross section of the conventional impact-point regulating mechanism shown in FIGS.  1-3, wherein the regulating cover 10 is locked.  FIGS.  7 and 8 depict a cross section of the conventional impact-point regulating mechanism shown in FIG.  1-3, wherein the regulating cover 10 is unlocked for zeroing.  The conventional regulating mechanism for impact point includes the regulating cover 10, the scale ring 20, a base 30, a regulating bolt 40, a securing bolt 50 and a spring 60. 
The base 30 is fixed to a main body 5 of the sight, and the regulating bolt 40 is screwed in the base 30 and thus joined to the base 30, whereby the regulating bolt 40 is movable in the base 30 for regulation of impact points.  The scale ring 20 is disposed on an outer periphery of the base 30.  The regulating cover 10 includes a first ring gear 12, and the regulating bolt 40 includes a second ring gear 42.  The regulating cover 12 is capable of rotating the regulating bolt 40 through the first ring gear 12 engaging with the second ring gear 42.  The securing bolt 50 is fixed to a center of the regulating bolt 40.  The spring 60 and an abutting portion 14 of the regulating cover 10 are disposed in a gap between the securing bolt 50 and the regulating bolt 40.  The spring 60 is a compression spring with one end propped against a head of the securing bolt 50 and the other end propped against the abutting portion 14 of the regulating cover 10. 
When the sight is to be zeroed, the regulating cover 10 is pulled up and the spring 60 is compressed.  The regulating cover 10 continues to be pulled until the spring 60 is compressed completely.  At the same time the first ring gear 12 and the second ring gear 42 are separated to release the engagement of the regulating cover 10 and the regulating bolt 40, whereby the regulating cover 10 becomes rotatable and the zeroing process for the sight can be performed.  Referring to FIGS.  2, 7 and 8, when the zeroing process is completed, the regulating cover 10 is released and thus moved by the spring 60 until the first ring gear 12 engages with the second ring gear 42, whereby the regulating cover 10 engages with the regulating bolt 40 again as shown in FIGS.  3, 4 and 5. 
The spring force of the spring 60 depends on the parameters including the wire diameter, free height, effective coil number, etc.  When a larger spring force is required, the spring 60 is designed to occupy more space.  Thus, the positions of the regulating cover 10, the regulating bolt 40 and the securing bolt 50 need to be changed accordingly.  In other words, the layout of the mechanism near the spring 60 is necessarily changed when the design of the spring 60 is changed.