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tat weights. Each dart weight shall be known to relative. Dart head surfaces shall be free of nicks, scratches, or other irregularities. The shaft shall be attached to the center of the flat surface of the head with its longitudinal axis perpendicular to the surface. If an electromag- net is used, the shaft shall be made of material that is not magnetic and shall have a steel tip 12.7 mm (0.50 in.) long at the end held by the electromagnet. ;,2.1 For Method A. the dart head shall be 3$.10 = 0.13 mm 0.500 = 0.005 in.) in jiameter. It may be constructed of smooth. polished aluminum, phenolic. or other low-den- ;' tv in of similar hardness. 9.2.2 For Method B. the dart head shall be ;0.80 t 0.13 mm (2.000 t 0.005 in.) in diameter. It may be constructed of smooth. polished stainless steel or other material of similar durability. 5.3 Incremental Weights for Methods A and B shall be of stainless steel or brass and cylindrical in shape. Each shall have a center hole 6.6 mm (0.26 in.) in diameter. The thick- ness of each shall be adjusted to obtain the specified weight within =0.5 %. Suggested sets of weights are as follows: 5.3.1 For Method A. 31 -mm (.25 -in.) diam- eter weights. Number Weight. g 2 or more 5 3 fj 8 30 s Qo 5.3.2 For'4tethod B. 45 -mm (1.75 -in.) diam- eter weights. Number Weight. g 2 or more 15 s 45 s 90 5.3.3 Optionally, additional weights, each Ie02=0.5 cfor Method Aor180g=0.5% for `lethod' B. may be constructed for use if it is necessary to extend the missile weight beyond that attainable when using all weights in the standard set. 6. Test Specimens 6.1 Test specimens shall be large enough to extend outside the specimen clamp gaskets at all points. The specimens shall be representa- 89 • tive of the film under study and shall he taken from the sheet or tube in a manner representa- tive of sound sampling practice. This is to ensure that the whole of the sheet be repre- sented in the test unless such sampling consti. tutes a variable under study. 6.2 The specimens shall be free of pinholes. wrinkles, folds, or other.obvious imperfections. unless such imperfections constitute variables understudy. 7. Conditioning 7.1 Conditioning -Condition the test speci. mens at 23 t 2°C (70 to 77°F) and 50 = 5 % relative humidity for not less than 40 h prior to test in accordance with Procedure A of Methods D 618, for those tests where condi- tioning is required. In cases of disagreement. the tolerances shall be tl°C (t1.8°F) and t2 % relative humidity. 7.2 Test Conditions -Conduct tests in the Standard Laboratory Atmosphere of 23 = :°C (73.4 t 3.6°F) and 50 t 5 % relative humidity unless otherwise specified in the test methods. •In cases of disagreement, the tolerances shall be =I *C (t1.8°F) and t2 % relative humidity. 8. Preparation of Apparatus 8.1 Set up the apparatus for testing by Method A or by Method B. 8.1.1 For Method A select a dart with a 38.1 -mm (1.5 -in.) liarneter hemispherical head. For ;Method B. sclect a dart with a 50.8 -mm (2 -in.) diameter hemispherical head. 8.1.2 Energize the electromagnet and po,i- tion the selected dart vertically with the steel shaft tip inserted in the magnet adapter. Adiu.t the drop height (the vertical distance from the plane of a clamped specimen to the bottom surface of the dart head) to 0.66 m (_'6 in.) for Method A or to 1.52 m.(60 in.) for Method B (Caution -For safety reasons, remove the dart while making position adjustments.) 8.1.3 With a trial film specimen clamped between the specimen clamps and with no added weights on the dart, de -energize the electromagnet to release the dart and�obser%e the point at which the dart impacts the speci- men, catching the dart --alter it bounces off the film surface. If necessary, adjust the electro- magnet position so that. in repeated trials, the