Figure 2-51.  Flag and pole blade tracking. BLADE 7 0 ° $_{t}$o 8 0 ° Curtain Pole Line parallel to longitudinal axis of helicopter Leading edge Position of chalk mark (approximately 2 inches long) Curtain Blade Pole Handle Pole Curtain 1/2" max spread (typical) Approximate position of chalk marks Electronic Blade Tracker sequence with the rotation of the main rotor blades so that a  fixed target at the blade tips appears to be stopped. Each blade  is identified by an elongated retroreflective number taped or  attached to the underside of the blade in a uniform location.  When viewed at an angle from inside the helicopter, the taped  numbers will appear normal. Tracking can be accomplished  with tracking tip cap reflectors and a strobe light. The tip  The most common electronic blade tracker consists of  a Balancer/Phazor, Strobex tracker, and Vibrex tester.  [Figures 2-52  through  2-54]  The Strobex blade tracker  permits blade tracking from inside or outside the helicopter  while on the ground or inside the helicopter in flight. The  system uses a highly concentrated light beam flashing in  Figure 2-53.  Strobex tracker. Figure 2-52.  Balancer/Phazor. BALANCER MODEL 177M-6A DOUBLE FUNCTION A Channel B TEST PUSH FOR SCALE 2 TRACK A B COMMON MAGNETIC PICKUP X1 X10 X100 RPM RANGE RPM TONE PHAZOR 12 6 3 9 1 2 4 5 7 8 10 11 Meter Band-pass filter Phase meter RPM STROBEX MODEL 135M-11 Strobe flash tube RPM dial 2-32