for a long period of time. These variables make it necessary  for the pilot to constantly check the instruments and make  appropriate changes in airplane attitude using cross-checking  of instruments. Examples of cross-checking are explained in  the following paragraphs.  When the selected radial cross-check is used, a pilot spends  80 to 90 percent of flight time looking at the attitude indicator,  taking only quick glances at the other flight instruments (for  this discussion, the five instruments surrounding the attitude  indicator are called the flight instruments). With this method,  the pilot’s eyes never travel directly between the flight  instruments but move by way of the attitude indicator. The  maneuver being performed determines which instruments to  look at in the pattern.  [Figure 6-17] In the inverted-V cross-check, the pilot scans from the  attitude indicator down to the turn coordinator, up to the  attitude indicator, down to the VSI, and back up to the attitude  indicator.  [Figure 6-18] In the rectangular cross-check, the pilot scans across  the top three instruments (airspeed indicator, attitude  indicator, and altimeter), and then drops down to scan  the bottom three instruments (VSI, heading indicator, and  turn instrument). This scan follows a rectangular path  (clockwise or counterclockwise rotation is a personal  choice).  [Figure 6-19] This cross-checking method gives equal weight to the  information from each instrument, regardless of its  importance to the maneuver being performed. However, this  method lengthens the time it takes to return to an instrument  critical to the successful completion of the maneuver.  A beginner might cross-check rapidly, looking at the  instruments without knowing exactly what to look for. With  increasing experience in basic instrument maneuvers and  familiarity with the instrument indications associated with  them, a pilot learns what to look for, when to look for it,  and what response to make. As proficiency increases, a pilot  cross-checks primarily from habit, suiting scanning rate and  sequence to the demands of the flight situation. Failure to  maintain basic instrument proficiency through practice can  result in many of the following common scanning errors,  both during training and at any subsequent time. Fixation, or staring at a single instrument, usually occurs for  a reason, but has poor results. For example, a pilot may stare  Inverted-V Cross-Check Rectangular Cross-Check Common Cross-Check Errors Selected Radial Cross-Check Figure 6-17.  Radial cross-check. 6-11