PaperCAD: A System for Interrogating CAD Drawings Using Small Mobile Computing Devices Combined with Interactive Paper

Table 4

Interpretation of double-headed arrows.

Event	Correct	Incorrect
Correctly interpreted	233
Did not complete before timeout (U)		13
Did not pause before writing label (U)		1
Missing one arrowhead (U)		1
Not perpendicular to the datums (U)		1
Extension lines not parallel (U)		3
Did not draw extension line (U)		11
Did not realize that previously drawn extension line was not valid (U)		2
Datums not perpendicular (U)		5
Not recognized (S)		1
Extension line misinterpreted (S)		3
Misinterpreted as a single arrow (S)		15
Misinterpreted as missing a datum (S)		1
Misinterpreted as not perpendicular to datums (S)		14
Total	233	71

U: user error; S: system error.