Disclosed is an adjustable weighted exercise apparatus which in one implementation may include a base frame assembly attachable to a strap assembly for connection to a user, the base frame assembly including a base frame; a weight support member connected to the base frame and disposed to maintain a weight at a distance from the user. In one embodiment, a physical-vapor deposition target offset from the processing chamber central axis, such as a target having an annular shape and central opening, deposits a material on a substrate while leaving the central region of the processing chamber available for other deposition techniques, including a centrally located sputtering target, CVD showerhead, or ion source. The invention moreover relates to an optical instrument, in particular a digital microscope, to which the calibration method according to the invention can be applied. It can perform a signal detection function on the real and imaginary portions of the squared signal energy to produce a clear channel assessment signal that indicates whether a set signal type is present in the wireless channel. 1,3-dicarbonyl compound chelating agent, 0-25% wt.