Calculator will calculate the two output values.
Efficiency -- The efficiency of the collector. That is, (Collector Heat Output / Total Solar Input). The efficiency is calculated for the specific conditions you entered. You will find that the efficiency varies greatly for different conditions. The idea of the calculator is to give a feel for how the efficiency and output vary as the collector and the system design are changed.
Output -- This is the heat output of the collector per square foot of collector area per hour. This is the the output for the specific conditions you entered.