
 NAO CONCISE SIGHT REDUCTION FORM:
 www.nao.rl.ac.uk/data/na/napf4a_cropped.pdf


 INTERPOLATION OF Z2:

   IF Z2 TABLE DIFFERENCE IS GREATER THAN 2 OR 3 DEGREES,
     WHEN A OR F IS CHANGED ONE DEGREE, THEN INTERPOLATE.

     DT1 = (Z2F1 - Z2) * (FM/ 60)   
     DT2 = (Z2AF1 - Z2A1) * (FM/ 60)
     ZDT1= Z2 + DT1
     ZDT2= Z2A1 + DT2

     DF = (ZDT2 - ZDT1) * (AM/ 60)
     Z2C = ZDT1 + DF

     A IS UNROUNDED INTEGER WHOLE DEGREE    A OR LAT
     F IS UNROUNDED INTERER WHOLE DEGREE    F OR LHA OR T
     AM IS MINUTES PART OF A
     FM IS MINUTES PART OF F
     Z2   = Z2 FROM TABLE INPUT OF A   AND F      
     Z2A1 = Z2 FROM TABLE INPUT OF A+1 AND F 
     Z2F1 = Z2 FROM TABLE INPUT OF A   AND F+1 
     Z2AF1 = Z2 FROM TABLE INPUT OF A+1 AND F+1 
     Z2C  = Z2 LINEAR INTERPOLATED

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 Z2 INTERPOLATION FORMULA:

   ENTER: A, F
   GIVES: Z2

   H  = ARCSIN( COS(A) * SIN(F) )
   Z2 = ARCSIN( COS(F) / COS(H) )
   
   IF F > 90 DEG THEN Z2 IS NEGATIVE
   IF F IS NEGATIVE THEN Z2 = 180 - Z2       ( Hc IS MINUS )

