Global Interrupt Enable and disable sei() and cli() - Due equivalents?

Hardware Arduino Due
7

I believe I'm getting better results along these lines:

FanSpeed2 = 0;
interrupts();
// sei(); //Enables interrupts
delay (1000); //Wait 1 second

Calc2 = ((FanSpeed2 * 60)/2);
noInterrupts();
//cli(); //Disable interrupts

the resultant rpm seems more realistic...and two fans are much more similar in output.

thanks