Help with G54

Having a devil of a time with G54. I got it right a few times, did a new setup and forgot how I did it when I got it right. I'm ok with X and Y, but when I enter G1 Z 1.00 in the MDI, the spindle begins a journey to the center of the earth.

This is what I tried. First, I went to REF ALL, zeroed all three axis after which I run the spindle to the X and Y locations on my workpiece, enter 0.0000 for X and Y. For the Z, I bring the spindle to a 0.4995" rod on the surface of my workpiece then set the Z to +0.4995".

I can move the spindle to a random location, MDI G1 X0.000 Y0.000 and the spindle travels to the correct location. But for G1 Z1.000, it wants to go below the surface of the workpiece.

I know I'm doing it wrong. Maybe I forgot to code G54 before I coded the moves.

Thanks,
John