TM 1-1510-218-10 3C-56 (a)   Scratchpad.      The   scratchpad   is   a buffer  to hold all data for review prior to executing the input.  As data is keyed into the CDU with the keypad, the entered values are displayed within the scratchpad field at the bottom of the display.  Incorrect entries are cleared with the   CLR  key.    A  single   press clears the last character on the right.  Holding the  CLR key down clears   the   entire   scratchpad.      The   scratchpad   is cleared  automatically  when  the  system  accepts  valid inputs. (b)   Function Keys.  The labeled function keys are used to call up specific top-level pages of the CDU  and  to  simultaneously  dedicate  the  line  select keys     to     the     functions     indicated     on     that     page.   Exceptions are the   MARK,  DATA, and  M3  keys  that do not change the page but do initiate their respective functions.  Some  functions,  which  are  less  frequently used  in  flight,  are  accessed  through  the  index  (IDX) and  flight  plan  edit  (EDIT)  function  keys  and  then  via line  select  keys  on  the  respective  menu  page.    The Index    and    Flight    Plan    Edit    pages    are    shown    in Figure 3C-24 and Table 3C-14. (c)   Line  Select  Keys.    Line  select  keys can   be   used   to   access   lower   level   pages,   toggle modes  of  the  function,  enter  data  in  the  associated field, or copy data in the scratchpad.  When undefined line select keys are pressed, no operation is performed and no annunciation is displayed. When a label next to the line select displays an outward  pointing  arrow,  selecting  the  line  select  will access the page identified by the line select label. When  a  colon  is  displayed  next  to  a  line  select label,   selecting   the   line   select  will  toggle  the  label value to a different state.  When two labels are shown, the toggled value is the innermost label or value. When brackets ([ ]) are displayed next to a line select, selection of the line select with valid data in the scratchpad will enter the data into the bracketed field and  enable  use  of  that  data  by  the  FMS.    When  the scratchpad is blank, selection of the line select next to the    bracketed    data    will    copy    that    data    to    the scratchpad. When  a  label  next  to  a  line  select  displays  an inward  pointing  arrow,  selecting  this  line  select  will either select, enable, or disable the indicated function or   item.      For   single   step   functions,   an   asterisk   to identify the function as enabled will replace the arrow.   When multiple selections are needed prior to activation of the function, a "fat" arrow to highlight the selection will replace the arrow.  When all selections are made, an asterisk will replace the fat arrow when the function is enabled. Symbolic aids are used to indicate what entries can be  made,  what  functions  are  on  or  engaged,  and what  selections  are  possible.    Refer  to  Figure  3C-25 for a summary of these symbols. NOTE The  lateral  and  vertical  scroll  arrows  are located   next   to   the   scratchpad   on   the display. (d)   Display  Scrolling.    Often  more data is available than what fits on a single display page.  In these cases display scrolling is used to access all the related information. Two types of scrolling are page scrolling and line scrolling.    Vertical  scrolling  with  up  (- )  and  down  (¯ ) arrows    either    accesses    additional    pages    of    the information   shown   or   scrolls   through   lists   of   data.   Horizontal  scrolling  with  left  (¬ )  or  right  (® )  arrows accesses additional pages of similar information. Holding  the  arrow  keys  causes  the  scrolling  to continue  until the key is released.  Special characters (horizontal    double-headed    arrow,    vertical    double- headed arrow, and multi-headed arrow) are displayed next to the scratchpad to indicate the type of scrolling. (e)   Confirmation   Function.      Functions that   involve   destruction   of   significant   internal   data require  confirmation  before  execution.    A  message, CONFIRM  XXX,  will  appear  in  the  scratchpad,  where XXX   is   a   message   unique   to   the   item   requiring confirmation.   The  scratchpad  message  is  cleared  by either   reselecting   the   appropriate   line   select   key   to confirm the selection or by pressing the  CLR key if the function is not desired. (f)    Copying and Transferring Data.   Most  data  to  be  entered  on  the  CDU  can  be  copied into the scratchpad in its original form by pressing the adjacent line select key, except where other operations    are    performed    which    take    precedence.   Once  copied  into  the  scratchpad,  this  data  may  be transferred elsewhere in the FMS-800.  For example, a waypoint may be transferred from the mark point list to the  flight  plan,  or  the  flight  plan  waypoint  sequence may    be    reordered    without    having    to    re-enter   the waypoint data.