A test mass can be made from a 2 cm x 1 cm piece of a manila folder. Fold the small piece lengthwise and then end for end to make a small tent that will stand up on the boom.
I estimated the weight of this mass in the following way:
Weight of 10 folders: 8 oz or 8*28.349 gm
Size of each folder: 29.8 cm x 45.0 cm
Weight of 2 cm2 = 28.35*8*2/(29.8*45*10) = 0.0338 gm