There  is a wealth  of human  factors  data  available  in the  literature.   Some references are  noted   in  the bibliography. The  type  of  information    which   might  be  needed   for a machine design  problem  ranges  from  dimensions  of the  human  body  and  their distribu- tion among the population by age and  gender,  to the  ability  of the  human  body  to with- stand  accelerations  in various  directions,  to typical  strengths   and  force  generating   abili- ty in various  positions.   Obviously,   if you  are  designing   a device  that  will  be  controlled by a human (a grass shortener, perhaps), you need to know  how  much  force  the user  can exert with hands  held  in various  positions,  what  the  user's  reach  is, and  how  much noise the ears can stand  without  damage.  If your  device  will  carry  the user  on it, you need data on the limits of acceleration which the  body  can  tolerate.  Data  on  all these  topics exist. Much of it was developed by the government which regularly tests the ability of military personnel   to  withstand   extreme   environmental   conditions. Part  of  the  background  re- search   of  any  machine   design   problem   should   include   some  investigation of human factors.

1.9 THE ENGINEERING REPORT

Communication of  your  ideas   and  results   is  a  very  important    aspect   of engineering. Many engineering students picture themselves  in professional  practice  spending  most  of their time doing calculations of a nature similar to those they have done as  students. Fortunately, this is seldom  the case,  as it would  be very boring.  Actually,  engineers  spend the largest percentage  of their  time  communicating  with  others,  either  orally  or  in writ- ing.  Engineers  write  proposals  and  technical  reports,   give  presentations,   and   interact with  support  personnel  and  managers.   When  your  design  is done,  it is usually  necessary to present  the  results  to your  client,  peers,  or employer.    The  usual  form  of  presentation is a formal engineering report. Thus, it is very important for the  engineering  student  to develop  his  or her  communication    skills.   You may  be  the  cleverest  person   in the world,

but  no  one  will  know  that  if you  cannot  communicate   your  ideas  clearly  and concisely.

In fact, if you cannot explain what you have  done,  you probably  don't  understand  it your- self.  To give you  some  experience  in this  important   skill,  the  design  project assignments in later  chapters  are  intended  to be  written  up  in  formal  engineering  reports.  Informa- tion on the writing of engineering reports can be found in the suggested readings in the bibliography   at the  end  of this  chapter.