An alternate method of sand calibration uses a container of known weight, such as a Proctor mold. In this method, you first weigh the mold and the attached base plate. Then, after attaching the mold collar, you pour the sand through the sand cone into the mold. Next, you remove the collar, strike off the excess sand, brush off the outside of the mold and base plate, and weigh the sand-filled mold (with the base plate attached). The difference in weights (filled and empty) divided by the known volume of the mold is equal to the density of the sand. The third calibration  (surface  calibration)  is discussed as part of the site preparation since it must be performed at the test site. SITE PREPARATION.— Site preparation con- sists  of  preparing  the  test  surface,  seating  the  template tray, and surface calibration of the tray. Begin your site preparation by choosing an area of the compacted surface that appears most level. You may have to remove some loose debris; however, make no attempt to pack or smooth the surface. Next, you seat the template tray flush on the surface, especially around the center hole. If necessary, seal any spaces around the center hole of the tray with modeling clay. Then force nails through the holes in the tray to hold it firmly in place.  Now  you  are  ready  to  perform  the  surface calibration. Surface  calibration  accounts  for  surface  irregu- larities of the area to be tested. With the valve closed, turn the sand-filled apparatus over and place the large cone over the center hole of the template tray. Open the valve and allow the sand to pass through until the large  cone  is  completely  filled.  Do  NOT  shake  or vibrate the apparatus. Then close the valve, weigh the apparatus with the remaining sand, and enter this weight on line 8 of DD Form 1215 (fig. 13-6A). The difference between the initial weight (line 7) and the final weight (line 8) is the weight of the sand that passed through the cone valve into the lower cone and the  center  hole  of  the  template.  Enter  that  weight  on line 9. After performing the surface calibration, recover as much of the sand from the tray as possible without disturbing the template tray or the soil in the hole. Brush the remaining sand particles lightly from within the tray. Leave the template in place for the volume- of-hole determination to be discussed next. VOLUME-OF-HOLE  DETERMINATION.— The  volume-of-hole  determination  consists  of  digging out a soil sample through the center of the template and computing the volume of the resulting hole. The hole that is dug through the center hole of the template  tray  should  be  about  6  inches  deep  and approximately the same diameter as the hole in the tray. When digging, keep the inside of the hole as free from  pockets  and  sharp  protuberances  as  possible. Make sure that  ALL material  removed  from  the  hole is placed in a container of known and recorded weight (line 23, fig. 13-6B). Keep the lid on the container as much as possible to prevent excessive moisture loss until it is weighed. When all removed material has been placed in that container, immediately weigh it and record the weight of the container and the material on  line  15.  Mark  the  container  for  later  identification when  the  soil  moisture  content  is  determined. Next, place the sand-cone apparatus over the hole in the tray and open the valve to allow the sand to flow into the hole that you have just dug. When the sand stops flowing, close the valve and weigh the apparatus with its remaining sand. Record this weight on line 11 (fig. 13-6A). The weight of the sand required to fill the  hole  and  the  volume  of  the  hole  can  then  be determined by following the instructions printed on the data sheet. DENSITY DETERMINATION.—  Now that you have  determined  the  volume  of  the  hole,  the  only remaining requirements are to determine the moisture content and the dry density of the sample that was removed  from  the  hole.  The  moisture  content  should  be determined  using  the  oven-dried  method  that  you studied in the EA3 TRAMAN. Lines 15 through 21 of DD  Form  1215  (fig.  13-6B)  are  used  to  record  the moisture-content  data. The  wet  density  or  unit  weight  (line  25)  is computed  by  dividing  the  wet  soil  weight  (line  24)  by 453.6 to convert the grams to pounds and then by the volume  of  the  hole  (line  14,  fig.  13-6A).  The  dry density  or  unit  weight  is  then  computed  using  the formula shown on line 26 of DD Form 1215. Nuclear  Moisture-Density Meter  Method Another  method  for  determining  the  moisture content  and  density  of  in-place  soil  uses  a  nuclear 13-8