Just dragging up some old IGES file references:
Suggested Technique For Analyzing A (Pro/ENGINEER) IGES File
Determining the Accuracy of an IGES File
Accuracy value is parameter 19, in this case 0.0234.
1H,,1H;,6HBLOCK2,12Haccuracy.igs, G 1
49HPro/ENGINEER by Parametric Technology Corporation,7H2000030,32,38,7, G 2
38,15,6HBLOCK2,1.,1,4HINCH,32768,0.5,13H000426.095310, 0.0234, 234., G 3
9Hlatkinson,7HUnknown,10,0,13H000426.095310; G 4