o<auto_zref> sub
o100 if [#<_task> EQ 0]
        (debug, Task is Null)
o100     return [999]
o100 endif

o200 if [#<selected_tool> EQ 0]
o200     return [1]
o200 endif

M6 (use builtin behaviour)

o300 if [#<_hal[gscreen.use_autozref]> EQ 0]
o300     return [1]
o300 endif

o400 if [#<_hal[gscreen.search_vel]> LE 0]
o400 return [-1] ; indicate search_vel <= 0 
o400 endif

o500 if [#<_hal[gscreen.probe_vel]> LE 0]
o500 return [-2] ; indicate probe_vel <= 0 
o500 endif

G21 (use metric units)
G49 (cancel tool offset)
G10 L2 P0 Z0 (clear current offsets)

(go to tool sensor location)
G53 G0 X[#<_ini[TOOLSENSOR]X>] Y[#<_ini[TOOLSENSOR]Y>]
G53 G0 Z[#<_ini[TOOLSENSOR]Z>]

(switch to incremental mode)
G91
(this section commented out for sim)
;G38.2 Z#<_ini[TOOLSENSOR]MAXPROBE> F#<_hal[gscreen.search_vel]>
;G0 Z4 (move up 4)
;G38.2 Z-4.1 F#<_hal[gscreen.probe_vel]>

;o600 if [#5070 EQ 0]
;     G90
;o600 return [-3] ; indicate probe contact failure to epilog
;o600 endif

(this section is used for sim)
G0 Z#<_ini[TOOLSENSOR]MAXPROBE> F#<_hal[gscreen.search_vel]>
(pretend that probe contact has been made)
G10 L20 P0 Z[#<_hal[gscreen.sensor_height]> - #<_hal[gscreen.block_height]>]
G90
G53 G0 Z#<_ini[CHANGE_POSITION]Z>

(signal success by returning a value > 0:)
o<auto_zref> endsub [1]
M2