Fig. 1From: Proficiency testing of skin prick testers as part of a quality assurance systemThe coefficient of variation of 8-double histamine wheal areas. a depicts the results of 3 mg/ml; b 10 mg/ml; c 30 mg/ml and d 100 mg/ml histamine. The solid line indicates the upper limit (CV < 40 %) for acceptance (4,5) while the dotted line represents the CV of 20 % (highly qualified tester)Back to article page