The Agilent R382A waveguide variable attenuator has an attenuation value that depends on the rotation angle of the resistive card, rather than on the resistivity value of the attenuating material. Therefore, it is insensitive to changes in temperature and humidity which can affect the resistive card of ordinary adjustable flap attenuators. The attenuation value is highly accurate and is stable from 0 to 50 dB. The instrument features large, easy-to-read dials, and can handle considerable microwave power.