These transparent, tempered-glass panels have a reference grid to enable precise adjustments to be made to wave-soldering machines. Glass panel is loaded either into a holding fixture or directly into conveyor to simulate a board passing over fluxer, pre-heater and solder-wave. The pattern of flux and solder coverage can be observed from the topside. The glass panel can be momentarily stopped to make machine adjustments. Factors such as immersion depth, flux and solder distribution and uniformity, contact angle and wave stability are easily monitored and controlled. Optional edge brackets are available for adapting 1/8" and 3/16" thick panels to 1/16" holding fixtures.