title: dsPic33 or PIC24, how accurate float (32bit) and double (64bit) using arctan
body: <p>Angle= arctan(BY/BX) </p>
  
  <p>I'm curious to know how accurate the trig calculation by Math.h library by above equation. </p>
  
  <p>I have read the manual and not clearly specified its accuracy. I have looked into google search but no clear answer is found. </p>
  
  <p>When angle goes toward to 0deg where numerator (BY) is small and denominator (BX) is large, where the By/BX term has low value, how the float (32 bit) and double (64 bit) is affected by this?. </p>
  
  <p>I know 64 bit is more accurate but need to see performance difference between 32 bit and 64 bit floating point (0deg to 90deg) by this dsPIC33 or PIC24 MCU.</p>
  
  <p>Is there rule how to use arctan for accurate calculation. One source suggest to work on 0deg to 45deg (0 to pi/4) for each 1/8 segment, this only apply to tan rather than arctan, correct?</p>