how to make exact delay in c18 compiler

// if Fosc=16MHz 

void Tempo_1mS()
{
asm{        
          MOVLW 210 ;
          MOVWF _N1;   // 8 bit counter
 ici:        
             nop ;   //1
        nop ;
        nop ;
        nop ;
        nop ;
        nop ;
        nop ;
        nop ;
        nop ;
        nop ; //10
        nop ;
        nop ;
        nop ;
        nop ;
        nop ;
        nop ; //16
        decfsz _N1 ,F ;   //decr counter, skip over next instruction if equal to zero  
        bra ici   ;
        nop;
        nop;
        nop;
        nop;  // add 4x0.25=1µS to round tempo pile poil to 500µS
 } ;
 }

// PIC18F serie : il faut timer0 sur 16 bits 
// delais pour FOSC=16Mhz


void Delay_uS(unsigned int x);
void Delay_mS(unsigned int cnt);
void Delay_1S(void);


void Delay_uS(unsigned int x)
{unsigned int y;
 y=x;   
while(--y != 0);
 }




void Delay_mS(unsigned int cnt)
{
  #ifdef DEBUG
  return;
  #else  
    
  INTCONbits.TMR0IE=0;     // no interrupt
  T0CON=0b00000001;  // Timer OFF, 16bits, internal, prescaler=1:4
  TMR0H=0xFC; //hi(64537);      // 1.0mS avec 1:4
  TMR0L=0x19; //lo (65537);
  while(cnt>0)
  { 
  T0CONbits.TMR0ON=1;
  while(INTCONbits.TMR0IF == 0); // wait over
  INTCONbits.T0IF=0;
  cnt--;
  TMR0H=0xFC; //hi(64537);      // 1.0mS avec 1:4
  TMR0L=0x19; //lo (65537);
  }
  T0CON=0;
  #endif


}


void Delay_1S(void)
{
  INTCONbits.TMR0IE=0;     // no interrupt
  T0CON=0b00000111;  // Timer OFF, 16bits, internal, prescaler=1:256
  TMR0H=0xC2; //hi(49911);      // 1.0 S avec 1:256
  TMR0L=0xF7; //lo (49911);
  T0CONbits.TMR0ON=1;
  while(INTCONbits.TMR0IF == 0); // wait over
  INTCONbits.T0IF=0;
  T0CON=0;
    TMR0H=0xC2; //hi(49911);      // 1.0 S avec 1:256
  TMR0L=0xF7; //lo (49911);
}