Choosing the appropriate number of levels for a continuously measurable factor is a difficult task and requires additional considerations. If the purpose of the factor is exploratory, two levels set at the extreme boundaries of the feasible operating range may be sufficient in determining if it is of any importance. If the basic concern is what needs to be monitored and controlled, two levels are also usually sufficient. If the purpose of the factor is for fine tuning optimum conditions, more than two levels will provide greater insight into selecting better levels for achieving the experiment objectives (Peace, 1993).

In the absence of exact nature of relationship between the independent variable and the performance parameter, one could choose 2 level settings. After analysing the experimental data, one can decide whether the assumption of level setting is right or not based on the percent contribution and the error calculations. TeVA, the Solar EVA Molten time is the time taken to ensure that the EVA is completely molten inside the laminator. If this time is too short the EVA will capture air pockets and therefore create voids at the interface, too long a time will cause the EVA to prematurely solidify and post cure which can lead to insufficient adhesion to the backing cover. Tpc, Post Curing time is the time taken to allow the EVA to solidify while a pressure is applied to the laminate. If this time is too long the EVA will start to crystallise, too short a time will jeopardise the gel content, which in turn affects the integrity of the laminate. Published reports indicate that of all the factors that affect Thermal Interface Resistances, the laminate Teva is the probably the most crucial. Therefore Teva was set at three levels and Tpc at two. The operating temperature is also set at three levels.