G20 G90 G17
(Source basis: LinuxCNC unit_tests/interp/test_interp_basics.cc Convert G20 / G21 verifies that current linear axes rescale on unit changes while rotary axes keep angular values.)
G0 X1 Y2 Z3 A4 B5 C6
G21
G0 X25.4 Y50.8 Z76.2 A4 B5 C6
G20
G0 X1 Y2 Z3 A4 B5 C6
M30