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Fig. 13 | Malaria Journal

Fig. 13

From: How many holes is too many? A prototype tool for estimating mosquito entry risk into damaged bed nets

Fig. 13

Three ellipses representing types of holes on a bed net each superimposed on a ½ cm grid for purposes of hole measurement. Widths of mid-point of each 1 cm section indicated in mm. a A large open ellipse with major axis = 120 mm and minor axis = 50 mm. Perimeter ~289 mm; area = 4710 mm2. Hole width is greater than ½ cm at all points along its length meaning that the risk assessment tool considers all parts of the hole passable (green crosshatch) for An. gambiae. Average hole width = sum of mid-point widths for all 1 cm sections/# of sections >½ cm wide = 36 mm. b Longer narrower elliptical hole with major axis = 120 mm and minor axis = 8 mm. Perimeter ~267 mm; area = 754 mm2. Two 1 cm sections at each end (red crosshatch) have mid-point widths less than or equal to ½ cm and are considered impassable by the tool. Average hole width = 7 mm. C. Very narrow elliptical hole with major axis = 120 mm and minor axis = 5 cm. Perimeter ~267 mm (by formula) or 240 mm by doubling length (see text); area = 471 mm2. None of the hole’s 1 cm sections has a mid-point width >½ cm meaning that the tool considers the entire hole impassable (red crosshatch); average width = 0 mm. NOTE: In cases where a hole, irrespective of actual shape, does not have a section width dimension >½ cm, time need not be wasted measuring its width

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