the overview of a preferred embodiment incorporating a neutral buoyancy auto - balancer in accordance with the present invention for scuba diving is shown in fig1 . the positional relationships between the neutral buoyancy auto - balancer in accordance with the present invention with an air cylinder 8 for dive and a regulator ( second decompression valve ) 211 is shown in fig2 . now reference is made to fig1 a cylinder 1 comprises a cylindrical body 11 and hemispherical circular end - plates 12 and 13 at the both sides of the cylinder . each of central holes 121 and 131 of the end - plates 12 and 13 at both side of the cylinder 1 may rotatably support a shaft 14 with intervention of bearings 122 and 132 ( see fig3 ) incorporating waterproof means 123 and 133 . the shaft 14 has , as can be most explicitly seen from fig5 and 6 , at its central portion , a weight 4 mounted thereon which extends radially outwardly in the cylinder 1 from the base on the shaft 14 , in one side of the base of which fixed is a tubing 21 forming the base of an inlet duct 2 , in other side of the base of which fixed is an inner tubing 31a forming the base of an outlet duct 3 for both air evacuation and the feed and drainage of water , which the inner tubing 31a is in turn slidably rotatably fitted to an outer tubing 31 . the shaft 14 mounted between respective central holes 121 and 131 on the end - plates 12 and 13 at both sides of the cylinder 1 is formed so as to arrange the tubing 21 of the inlet duct 2 , the base of the weight 4 , and the inner tubing 31a and outer tubing 31 of the outlet duct 3 , in its longitudinal axis . the inlet duct 2 is fitted at its base to a notch of said tubing 21 . in the opposite direction of approximately 180 degrees of the projection of the weight 4 , a nozzle 22 is formed protruded therefrom in the cylinder 1 . in addition , the inlet duct 2 is communicating with the tip of an exhaust tube 212 from the regulator 211 ( see fig2 ) outside the cylinder at the central hole 121 . this allows to exhaust air from the regulator 211 to pass through the tubing 212 , central hole 121 , and tubing 21 , and to eventually be introduced into the cylinder 1 via the nozzle 22 of the inlet duct 2 as shown by an arrow line 23 in fig6 . the outlet : duct 3 for both air evacuation and feed and drainage of water is , as shown in fig5 and 6 , rotatably circumferentially slidably fitted at its base in the range of alignment of respective notches of the inner tubing 31a and the outer tubing 31 . an inlet port 32 of the outlet duct 3 is opened in a direction radially outwardly aligned with the projection of the weight 4 in the cylinder 1 . in this way , the outlet duct 3 may drain water and / or air in the cylinder 1 from the inlet port 32 through the inner tubing 31a , the outer tubing 31 , and a central hole , namely an exhaust opening 131 , to the outside in case in which the internal pressure of the cylinder 1 become elevated with respect to the water pressure of surrounding environment , while on the other hand the outlet duct 3 may introduce into the cylinder 1 some free water passing from outside through the central hole 131 , the outer tubing 31 , and the inner tubing 31a to the inlet port 32 , in case in which the internal pressure of the cylinder 1 become reduced with respect to the water pressure of surrounding environment . an angular displacement adjusting means of the inlet port 32 with respect to the weight 4 is arranged to secure , as clearly shown in fig3 and 4 , a gear box 611 axially supporting a worm ( spiral ) gear 61 at the outer surface of the end - plate 13 at another side , with a knob 612 being provided at the end of the shaft 14 extended from the gear box . the angular displacement adjusting means also secures a worm wheel 62 at the outer periphery of the outer tubing 31 so as to engage the worm wheel 62 with the worm 61 . in this way , when a diver rotates with his / her finger the knob 612 , the worm 61 spins and the worm wheel 62 engaged thereto rotates accordingly to displace the outlet duct 3 integrated therewith at the center of the inner tubing 31a . the inlet port 32 located at the remote end of the outlet duct 3 moves spaced apart to a desired degree from the radial axis of the weight 4 ( see fig7 through 11 ). as a result , the inlet port 32 may be positioned at a level elevated by any desired height from the vertical level designated by the weight 4 . operation of the device will be described below in greater detail . an initializer means 5 for initializing water level in the cylinder 1 in accordance with the variation of buoyancy including the body weight of scuba diver comprises , as shown in fig1 and 3 , an air bleeder tubing 50 extendingly mounted from the central hole 121 on the outer surface of the endplate 12 at the one end , at the tip of which is provided a bleeder valve 51 , and a button 52 for opening and closing the bleeder . if the button 52 is pressed by a scuba diver at the surface level of water pressure 1 atm ., the bleeder valve 51 is opened to purge air in the cylinder 1 through a valve 51 and a tubing 50 to the environment . at the same time some water is introduced from an outlet port 311 through inlet port 32 into the cylinder 1 , so as to set water level 53 corresponding to the water pressure 1 atm . for that scuba diver in the cylinder 1 when the diver &# 39 ; s whole body completely sinks under water . in fig1 and 2 , reference numeral 7 designates to an attachment for attaching the neutral buoyancy auto - balancer to the chest of diver , numeral 8 to the air cylinder , 81 to a first pressure reducing valve , 82 to a fathometer and a pressure gauge , 211 to the regulator ( second pressure reducing valve ), 212 to the exhaust tubing connecting the regulator to the central hole 121 of the neutral buoyancy auto - balancer . with the neutral buoyancy auto - balancer of such arrangement as described above , the functionality of its components when a diver initializes level - in - cylinder , sinks from the surface , and raises from deep level under water will be described below in greater detail in this order . for preparation of diving , as shown in fig2 a diver first attaches firmly the neutral buoyancy auto - balancer on the chest or abdomen by using the attachment 7 , carries on his / her back an air cylinder 8 , connects the tip of tubing 212 of the regulator 211 to the central hole 121 of the end - plate 12 in one side of the neutral buoyancy auto - balancer , and zeroes the angle of the inlet port 32 in the cylinder 1 with respect to the weight 4 . then the diver enters into the water . as the cylinder 1 is fulfilled by air , it provides sufficient buoyancy for the diver to permit to float on the surface of the water . next , in order to initialize the water level 53 in the cylinder 1 before sinking , pressing the button 52 causes air in the cylinder 1 to bleed through the valve 51 and tubing 50 into the environment , while at the same time it causes some water to be introduced from the outlet port 311 through the inlet port 32 . when the whole body of a scuba diver is completely sunk under water , water and air will be balanced at the water level 53 at the water pressure 1 atm . corresponding to the buoyancy of that diver . the level 53 is at this point attained to a level higher than the position of the inlet port 32 of the outlet duct 3 , as shown in fig3 and 4 . at this point the diver releases the button 52 to close the bleeder valve 51 so as to prevent leakage of air in the cylinder 1 and operates the knob 612 to spin the worm 61 to rotate the worm wheel 62 engaging therewith so as to gradually increase the relative angle between the integrated outlet duct 3 and the weight 4 . since the weight 4 stays in vertical position due to its weight , the inlet port 32 of the outlet duct 3 displaces in the lateral direction , eventually to the location at which the port reaches to the water level 53 . if the knob 612 is released at the time that the diver confirms the outlet duct 3 have reached to that position , for example by observing through a viewing glass 111 , as shown in fig1 and 2 , the outlet duct 3 will stay at that angular position due to worm engagement . in such a way the angular adjustment of the inlet port 32 corresponding to the initial level in the cylinder 1 is completed . thereafter , air introduced into the cylinder 1 through tubing 212 of the regulator 211 will be bled , passing through the inlet port 32 and then the outlet port 311 of the outlet duct 3 to the outside in the water as excessive supply , so that the balance of air and water in the cylinder 1 will remain unchanged , and maintain the adjusted neutral buoyancy . now , diving is ready to go . there are two ways of diving for the neutral buoyancy auto - balancer according to the present invention : first , air - bleed diving method which is performed by continuously pushing the button 52 of the bleeder valve 51 to purge air from the cylinder 1 and introduce water from the outlet port 311 into the cylinder 1 to decrease buoyancy of the cylinder . second , fin diving method which is performed by using fins to go down in position upside - down . in the air - bleed diving method , exhaust gas made by the respiration of diver and supplied from the regulator to the cylinder may temporarily increase buoyancy of the device . however , excessive amount of air beyond the range of neutral buoyancy may not reside in the cylinder ; excessive air will be purged through the outlet duct 3 to the outside . even though the diving rate may be slightly slowed down , this method assures not to upwardly climb . when the button 52 of the bleeder valve 51 is released for staying at a given desired depth , it is conceivable that the amount of air residing in the cylinder 1 may become temporarily insufficient for an instant to cause a negative buoyancy ( see fig7 ). however continuous introduction of air from the regulator will quickly create buoyancy sufficient to stabilize ( see fig8 ) excess water which invaded the cylinder 1 is pressed out of the cylinder 1 through the outlet port 32 by means of natural breath as described in the above discussion relating to fig . 14 . in fin diving method , increasing depth may introduce , as shown in fig7 some negative buoyancy for a short time of period to cause increase of water level 531 and acceleration of diving rate . however continuous introduction of air from the regulator will quickly recover the water level into the water level 53 to obtain neutral buoyancy , as shown in fig8 . the most significant characteristics of the fin diving method is that a diver is in position upside - down , i . e ., legs are up and head is down . in this situation the neutral buoyancy auto - balancer attached to the chest and / or abdomen of diver also is forced to be in anteversion or retroversion , as shown in fig1 and 11 , about the axis 14 . for the neutral buoyancy auto - balancer in accordance with the present invention , when the attachment 7 is inclined in front or back at . for example , forty - five degrees as shown in fig1 , ninety degrees as shown in fig1 , and hundred - thirty - five degrees or hundred eighty degrees ( not shown ) about the shaft 14 on the center line of the cylindrical body 11 , the weight 4 in the cylindrical body 11 remains in vertical position so that the inlet port 32 of the outlet duct 3 keeps a predetermined angular position with respect to the vertical weight 4 . accordingly the interface of water and air , the water level 53 in the cylinder 1 , moves and stays in the same vertical direction as the weight 4 because water is always heavier than air . the inlet port 32 at a desired angular position is in turn brought to a location of the interface of water and air , so as to be always able to reside in a desired water level 53 , to purge water up to the level if amount of water is excessive , and to purge air up to the level if amount of air is excessive , in order to perform the functionality of holding the water level to a predefined level , i . e ., holding neutral buoyancy . when upwardly moving under water , water pressure in the cylinder decreases , leading to inflation of air in the cylinder accordingly , thus temporary positive buoyancy . however the neutral buoyancy auto - balancer quickly recovers neutral buoyancy because excessive air will be immediately purged from the inlet port 32 to the outside . when reached to the surface , by operating an angular position adjusting knob 612 to readjust the angular displacement of the outlet duct 3 to align with the weight 4 to position the inlet port 32 at the lowest height in the cylinder , most water in the cylinder 1 will be purged , the cylinder 1 will be fulfilled with air so that the buoyancy of neutral buoyancy auto - balancer will become maximum to help a diver floating on the surface . now reference is made to fig1 and 13 , there is shown an alternative embodiment of the present invention , comprising , instead of an angular displacement adjusting means 6 of the outlet port 32 for operably adjusting the outlet port 32 with respect to the weight 4 at any desired angle as mentioned above , a radial adjustment means 6a of the outlet port 32 for adjusting the outlet port 32 along with its radial direction from outside . fig1 illustrates the inlet port 32 displaced inwardly along its radial direction ; fig1 illustrates the inlet port 32 displaced outwardly along its radial direction . in this embodiment the outlet duct 3 is replaced with a flexible tube 63a , inlet port 32 provided at the tip of the tube is made adjustable from outside by means of a combination of worm and arm mechanisms . more specifically , the inlet port 32 positioned at the tip of a flexible tube 63a is supported by a free end of an arm 622a . the base of the arm 622a is secured to a shaft 621a and a worm wheel 62a centered about the shaft 621a in a form of sector - of - a - circle is provided . a worm 61a engaging to the worm wheel 62a is mounted in a hollow tube which is concentrically arranged to the shaft 14 . the shaft 611a of the worm 61a is arranged so as to be projected from the outlet port 311 to the outside through the central hole 131 to provide a knob 612a at the projected end of the shaft 611a . in this way , a diver may rotate the knob 612a from the outside of the neutral buoyancy auto balancer to transfer rotational movement through the shaft 621a to the worm 61a , and then the worm wheel 62a engaging to the worm 61a is rotated around the shaft 621a to create angular displacement of the arm 622a extending from the shaft 621a . the free end of the arm 622a then displaces in its radial direction so that the inlet port 32 connected to the free end of the arm accordingly displaces along its radial direction . as have been described above , the neutral buoyancy auto - balancer according to the present invention require no adjustment during diving , except for the manual initialization of the water level in its cylinder at the water surface in an area of water pressure 1 atm . thereafter , during sinking , staying at any given depth , and climbing , the neutral buoyancy auto - balancer automatically operates , only by means of introduction of air used by the respiration of a diver into the cylinder , to maintain neutral buoyancy . many trouble caused by the misoperation of divers may be avoided and divers may work under water without risk and perplex adjustment . in addition , the neutral buoyancy auto - balancer according to the present invention is formed as a cylinder about an axis , while inside , a weight extended from the axis directs in vertical direction regardless of circumferential displacement of the cylinder . by arranging air inlet port to be rotatable in inward and outward direction along its radial direction , when the cylinder is rotated or inclined in its circumferential direction , about its center axis , outlet port can be moved to accurately locate at or near the variable water level in the cylinder . using the neutral buoyancy auto - balancer according to the present invention provides divers with a significantly large degree of freedom with respect to their diving position , allowing for neutral buoyancy auto - balance under water in addition to the wide range of postures . although the present invention has been described in conjunction with several preferred embodiments thereof , it should be understood that these embodiments are disclosed by way of examples and the present invention is not to be limited thereto . it should be recognized that many changes and modifications may be made by those skilled in the art without departing from the true spirit and the scope of the present invention set forth in the appended claims .