Abstract: Disclosed is an apparatus for effecting precise thermal cycling of articles by alternately employing electrical heating elements and circulating cooling water in conjunction with a controller to accurately regulate the temperature of a working surface. The apparatus includes a thermal tray in which articles are mounted in recesses formed in the working surface region thereof. The thermal tray is removable from the base of the apparatus which houses the heating elements and cooling water. Thus, thermal trays are interchangeable atop the base as desired. Also disclosed is a weight assembly for maintaining the articles in the recesses. This allows the thermal tray of the present invention to be transported to each of a plurality of processing stations, including the aforementioned thermal processing atop the base, while still maintaining precise positioning of the articles throughout each of the processes.