The displayed curve and analytic measurement differ
For the supported XY center format, the viewer derives a center from I and J offsets relative to the start point. It checks start and end radii, determines clockwise or counterclockwise sweep and allows a simultaneous Z change for a helix.
The preview draws short chords for a responsive display. Reported arc length is analytic: radius times sweep, combined with the Z rise for a helix. The numeric length therefore does not depend on how many straight preview chords you see.
Units and modal inputs matter
G20 and G21 convert subsequent coordinates and explicitly supplied feed words into the internal millimeter representation. G90 and G91 select absolute or incremental XYZ targets. The supported I/J arc-center mode remains incremental.
The declared subset rejects unknown coordinate systems, other arc planes and unsupported arc syntax. A syntactically similar word in another controller dialect may have a different meaning; this viewer does not infer the dialect from a file extension.
Timing is a calculation under assumptions
Each feed movement contributes distance divided by its feed. Rapid movements use the speed entered in the form. G4 P contributes seconds. If a feed movement has no known feed, total ideal time is unknown rather than silently assuming a cutting speed.
This arithmetic omits acceleration, blending, spindle speed changes, tool changes and controller limits. Use it to compare a declared sequence under the same assumptions, not to promise a production completion time. The report includes the assumptions with the exported values.