To be deductible, a business expense must be both ordinary and necessary. An ordinary expense is one that is common and accepted in your trade or business. A necessary expense is one that is helpful and appropriate for your trade or business. An expense does not have to be indispensable to be considered necessary. It is important to separate business expenses from the following expenses:
A duple meter metronome that is useful for 2/4, 2/8, 2/2 (cut time), and 6/8 when it has two beats per measure.
If your riflescope has a duplex reticle where the distance between the intersection of the cross wires and the bottom taper point of the vertical wire equals 4 inches at 100 yards, it will equal 16 inches at 400 yards.