PS:
+-50 Cent makes sense, since it's half of a semitone interval, see
the Information taken from
http://www.sengpielaudio.com/calculator-centsratio.htm:
Interval Frequency ratio cents
Semitone or minor second 1.059463 : 1 100
Here's a Table of Cents Difference for some frequencies close around
440 Hz:
Frequency Difference
435 Hz −19.78 cents
436 Hz −15.81 cents
437 Hz −11.84 cents
438 Hz −7.89 cents
439 Hz −3.94 cents
440 Hz ±0 cent
441 Hz +3.93 cents
442 Hz +7.85 cents
443 Hz +11.76 cents
444 Hz +15.67 cents
445 Hz +19.56 cents
So, the conversion factor 4 cents / Hz is valid for the purposes of
tuning as an exception only very close around 440 Hz. There is no
conversion from Hz to cents and vice versa. Statement: Cent is a
logarithmic unit of measure of an interval, and that is a dimensionless
"frequency ratio" of f2 / f1.