shortages. For example, concrete ingredients, lumber, reinforcing materials, and everything else involved in mixing and placing the concrete, including equipment time,  manpower,  and  man-hours,  will  be  serious]  y underestimated and ordered. Checking  Estimates The  need  for  accuracy  in  checking  estimates  is vital. Check quantity estimates to eliminate as many errors  as  possible.  One  of  the  best  ways  for  you  to check  a  quantity  estimate  is  to  have  another  person make an independent estimate and then to compare the two.  Any  differences  should  be  noted  to  determine which is right. A less effective way of checking is for another  person  to  take  your  quantity  estimate  and check  all  measurements,  recordings,  computations, extensions, and copy work, keeping in mind the most common error sources (listed in the next section). Error  Sources Your failure to read all of the notes on a drawing or  failure  to  examine  reference  drawings  results  in many  omissions.  For  example,  you  may  overlook  a note  that  states  “symmetrical  about  the  center  line” and thus compute only half the required quantity. Errors   in   scaling   obviously   mean   erroneous quantities.   Great   care   should   be   taken   in   scaling drawings so that correct measurements are recorded. Common  scaling  errors  include  using  the  wrong  scale, reading the wrong side of a scale, and failing to note that a detail being scaled is drawn to a scale different from that of the rest of the drawing. Remember that some  drawings  are  not  drawn  to  scale.  Since  these cannot  be  scaled  for  dimensions,  you  must  obtain dimensions from other sources. Sometimes wrongly interpreting a section of the specifications causes errors in the estimate. If there is any  doubt  concerning  the  meaning  of  any  part  of the  specification,  you  should  request  an  explanation of that particular part. Omissions  are  usually  the  result  of  careless examination  of  the  drawings.  Thoroughness  in  examining drawings and specifications usually eliminates errors of omission. Use checklists to assure that all activities or materials  have  been  included  in  the  estimate.  When drawings  are  revised  after  material  takeoff,  compare  new issues  with  the  copy  used  for  takeoff  and  make  the appropriate  revisions  in  the  estimate. Construction  materials  are  subject  to  waste  and loss  through  handling,  cutting  to  fit,  theft,  normal breakage, and storage loss. A person’s failure to make proper   allowance   for   waste   and   loss   results   in erroneous estimates. Other   error   sources   are   inadvertent   figure transpositions, copying errors, and math errors. ACTIVITY  ESTIMATES The  crew  leader  is  responsible  for  making  sure  all required  resources  are  identified.  The  crew  leader must   estimate   materials,   equipment,   and   labor required  to  complete  each  construction  activity.  All required  resources  are  listed  on  CAS  sheets.  The scheduled start and finish dates for each activity are taken from the Level III bar chart and shown on the CAS sheet. The resources are then tied to the schedule, and any action required to track or request resources can be monitored on the CAS sheet. Master  Activities The Naval Construction Regiments (NCRs) usually assign  master  activities  to  the  projects.  The  master activities can be broken into at least five construction activities. Most commonly, master activities number between  eight  and  ten.  These  activities  identify functional parts of the facility and are often tied to a particular  company  or  rating.  It  must  be  clear  to  all personnel involved in the planning process exactly what work is included in each master activity. That is the purpose of the master activity listing. By providing a good  narrative  description  of  each  master  activity,  it  will be clear to all where each work element falls. A good narrative description reduces the chance of omitting any work items from the estimate. Master activities for a typical building might look like the following list of items: 2-26