A Sea Tech single wavelength (488 nm) absorption meter (known as the `a-meter') has been deployed in the Florida Straits and in the open ocean near Kauai, Hawaii. The instrument has been evaluated to assess its performance in measuring the diffuse attenuation coefficient (Kd) so that the numerous problems associated with traditional Kd measurements can be avoided. (Traditionally, one measures downwelling irradiance, which requires daylight and suffers from the effects of clouds, ship shadowing, instrument tilting, surface wave focussing, and Raman transpectral scattering.) The main result of this evaluation is that the a-meter generally provided profiles that agreed with traditional Kd profiles to within about 0.003/m, and the instrument did not suffer from any of the problems of irradiance measurements. It did, however, require the use of knowledgeable deployment, maintenance, and calibration techniques and the use of essential supporting measurements in order to obtain this degree of accuracy. This paper describes these aspects of how to effectively use the a- meter and provides representative examples of simultaneous traditional Kd profiles.