Hall Effect Sensor Maximum Speed?

Hi all,

I am using Mh 281, uni polar hall effect sensor, which switches on in the presence of magnet and switches off in the absence of magnet, and I am using the code

 volatile byte half_revolutions;
 unsigned int rpm;
 unsigned long timeold;
 void setup()
   attachInterrupt(0, rpm_fun, RISING);
   half_revolutions = 0;
   rpm = 0;
   timeold = 0;
 void loop()
   if (half_revolutions >= 20) { 
     //Update RPM every 20 counts, increase this for better RPM resolution,
     //decrease for faster update
     rpm = 30*1000/(millis() - timeold)*half_revolutions;
     timeold = millis();
     half_revolutions = 0;
 void rpm_fun()
   //Each rotation, this interrupt function is run twice

, I got this code from arduino playground, and my doubt is, what is the maximum rpm which can be detected using this hall effect I tried reading datasheet but in vain,
i.e. how many pulses can hall effect detect per second? I am using this for the measurement of crank shaft of two wheeler..

I tried reading datasheet but in vain,

See attached:-

It can't go faster than the rise and fall time.

Thanks man