TM 5-6635-386-12&P a. Place tester on prepared site so that the source tube hole is positioned reasonably close to the hole in the surface to be tested. b. Standing slightly behind the tester with your feet placed comfortably apart, flex your knees and bend your body slightly forward above the waist. c. Brace    your    right    elbow    on    your    right    knee, grasping the cast lip of the tester with the fingers of your right hand. d. Put your left hand on the source tube handle. e. Allowing  the  left  edge  of  the  tester  to  remain  in contact  with  the  surface,  lift  the  right  edge  of  the  tester two to four inches above the surface. f. Release   the   spring   lock   on   the   source   tube handle  with  your  left  thumb  and  push  the  source  tube down approximately 2 inches. g. Peeking over the front edge until you just see the end of the source tube, lower the right side of the tester and guide  the  source  tube  into  the  hole  in  the  prepared surface. h. Lower the source tube to the desired depth. 1-20.  TAKE A NUCLEAR READING ON SITE Once the site is prepared, a standard count is available, and the tester seated, a field count can be obtained. No   advantage   is   gained   from   repeating   a   count   on exactly  the  same  site.    It  is  permissible  to  rotate  the tester  900  or  more  on  a  site  to  obtain  two  views  of  the location,  but  there  is  nothing  to  be  gained  from  taking more  than  one  count  without  at  least  moving  the  tester. It   would   be   better   to   move   the   tester   to   another   site nearby  for  the  second  count  in  order  to  obtain  a  better representative sample of the overall project. Reviewing  paragraph  1-9  and  applying  these  statistical factors to the tester readings, we will observe that: a. The  tester  will  not  count  exactly  the  same  two times in a row except by coincidence. b. This  count  variation  is  a  function  of  the  random source decay. c. This will obviously produce a predictable error in the final result of PCF values. d. The    error,    identified    as    "Precision"    can    be charted as follows:  (1 minute counts) ±PCF BS Regular @ 120 PCF .60 BS (AC) @ 120 PCF .50 6" Trans @ 120 PCF .25 Moisture @ 15 PCF .25 This error is the tester’s repeatability.  The final accuracy obtained on the site is also a function of how accurately the  factory  calibrated  the  tester  and  how  carefully  the operator chose and prepared his site. The  value  of  the  final  result  is  also  a  function  of  how representative of the overall project the selected site is. Precision   is   also   influenced   by   the   selection   of   time period on the Operations Touchkeys: (in PCF) 1/4 1/2 1 2 BS 1.20 .85 .60 42 AC 1.0 .71 .50 .35 6" .50 .35 25 .18 Moisture .50 .35 .25 .18 Select the  time  touchkey  which  will  produce  the  desired precision versus time available for the test 1-21.  FIELD COUNTS AND TRANSMISSION a. Site is prepared, standard count recorded b. Seat tester firmly. c. Release source handle trigger and lower source to BS or AC position as desired. d. Press desired Operations Touchkey. 1-16