Using G-Code, Y0 is the center of the board

This is a strange issue. When I home the spindle the spindle moves to the left front corner and the z moves all the way to the top of the slider. If I send the G Code sequence “G90 G21 G0 X 450 Y0” to move the spindle to the front center of the board, the spindle moves to X450 Y 432.5. My carve area is 900mm by 865mm. To move the Y to the front of the board I have to give a Y-432.5.

Home is not the same as work zero.
You need to set your work zero as all G90 (absolute) motion mode commands are relative to that origin.

Thanks Neil.
I homed the system and checked the work position and machine position. The machine position was
x = -889
y = -826

Work position
y= -908
z= -10

I reset the controller and the positions changed.
X = 0
Y = 0
Z = 0
Work position:
Y= -102.601
Z= 132.579

How do I set the work position using g-codes?.

@RonJohnson When you home, your machine should always end at the same position. Did you change anything in grbl before you downloaded it to your controller?
For most use cases, your machine position is simply a consistent reference location, based on your switches, for all of your offsets. The only thing that matters for your job is the work position (aside from some custom post processors using machine positions).

To set your work zero:
Home the machine
Jog to your desired work zero
Send G10L20 P1 X0Y0Z0

That will set the current position as your work origin for the G54 work coordinate system (default).

Thank you Neil.
I had used easel to set my work position. my total work area is 900mm X 865mm. When I home the machine It consistently moves to the left front of the waste board. I think I have everything under control now that I understand the work position is the reference. Thanks again.