Ok thanks for confirming, I figured as much.
Dt’s original timer, or a bastardised version of it, because I know for the project it will always be clocked at 10 MHz,
and I also know I will only ever be interested in 100 Hz interrupt form the timer. The portb.0 interrupt is simpler, and I’ve done that manually.

To answer your other question.. It’s still about synchronising the timer to a GPS PPS pulse, but I want to go better than simply resetting Ticks,
and load the timer correctly for that situation as well... So when the program decides to sync, it enables portb.0 int, resets the flag for portb.0 int,
and then the next rising edge interrupt should call the same timer where it is loaded and then the portb.0 interrupt turned straight back off
unless the program decides to do the sync again at some later time.

Dealing with the timer ISR.. it seems I could save myself some instruction counting, and deal with the timer value the same way the reload code does
by just making sure the next Tick will occur correct time, rather than dealing with the current portb.0 int Tick that called the ISR.

This is my first play.. not sure about it and haven’t thought about it too much.. it’s my first play in a compiler since I started talking to you.
I disable ext int just a little later when the time values are being incremented and timing isn’t as critical.
For this version the constant needs another 6 added to it.

For most of the time ext int is disabled it’s supposed to act as it normally would, but take a little longer to execute.

Code:
; -----------------  ADD TimerConst to TMR1H:TMR1L
ADD2_TIMER   macro
    CHK?RP  T1CON

     BCF     T1CON,TMR1ON       ; 1 Turn off timer
     MOVLW   LOW(TimerConst)    ; 1

     BTFSC   INTCON,INTE	; 1/2
     MOVWF   TMR1L		; 1/0

     BTFSS   INTCON,INTE	; 1/2
     ADDWF   TMR1L,F            ; 1/0

     BTFSC   STATUS,C           ; 1/2
     INCF    TMR1H,F            ; 1/0
     MOVLW   HIGH(TimerConst)   ; 1

     BTFSC   INTCON,INTE	; 1/2
     MOVWF   TMR1H    		; 1/0

     BTFSS   INTCON,INTE	; 1/2
     ADDWF   TMR1H,F            ; 1/0

     endm