G90 G17 G40 G80 G00 
S20000 M03 
#101=0 ; Start Z
#101=#101-#21
if [ #101 gt #11 ] 20
#101=#11 (if Step Z more than Depth Z, limit it)

N20 G0 X0. Y0. A0.
#102=[ #10 - #50] / 2; Last X corrected by Tool Radius

N50 G0 Z#60 
#100=#20 (Current X = Step X )

N100 G1 X#100 Y0. A0. 
G1 G94 Z#101 F#40
G3 X#100 Y0. I[0-#100] J0. F#41

if [ #100  GE #102 ]  200 
#100 = #100 + #20
if [ #100  LE #102 ]  100 
#100 = #102
JUMP 100

N200 G00 Z#60 

if [ #101 LE  #11 ] 500 (goto finish)
#101=#101-#21 (Current Z = Step Z )
if [ #101 GT  #11 ] 50
#101=#11
JUMP 50

N500
M05 
G90 
M30