measuring pulse width

i have that pdf and i understand that i need to capture the rising and falling edge.

but i dont understand the value of what registers i need to capture.

i have an example program of a 16-bit pwm going and while debugging, it goes into the isr on the rising and falling edge, but i dont know what register value to capture.

the configurations code is as follows:

PCA0MD = 0x02; 	// disable CF interrupt
					// PCA time base = SYSCLK / 4

	PCA0CPL0 = (0xff & PWM); 		// initialize PCA compare value
	PCA0CPH0 = (0xff & (PWM >> 8));
	PCA0CPM0 = 0x4d; 				// CCM0 in High Speed output mode
	EIE1 |= 0x08; 					// enable PCA interrupt
	EA = 1; 						// Enable global interrupts
	PCA0CN = 0x40; 					// enable PCA counter

void PCA_ISR (void) interrupt 9
{
	if (CCF0) {
		CCF0 = 0; // clear compare indicator
		if (PWM_OUT) { // process rising edge
			PCA0CPL0 = (0xff & PWM); // set next match to PWM
			PCA0CPH0 = (0xff & (PWM >> 8));
		} else { // process falling edge
			PCA0CPL0 = 0; // set next match to zero
			PCA0CPH0 = 0;
		}
	} else if (CCF1) { // handle other PCA interrupt
		CCF1 = 0; // sources
	} else if (CCF2) {
		CCF2 = 0;
	} else if (CCF3) {
		CCF3 = 0;
	} else if (CCF4) {
		CCF4 = 0;
	} else if (CF) {
		CF = 0;
	}
}