If the arc start point is to the right and above the center point I and J will both be negative. Three axis circular interpolation is supported, in G17 mode this means the mill will describe a helix. As the mill describes the 180 degree arc in the X-Y plane it will feed down to Z0. G03 Counter Clockwise arc. Same rules as G02 apply.
Resolution is in tenths of a second.
Note the use of the non-standard P variable. G17 Arcs in X-Y plane. This is the power-on default. I and J specify the center point. G18 Arcs in the X-Z plane.