Across-Stream In-situ Gas Analyzer Description By definition, "in-situ" measurements are made in place directly within the process. AIM is the leader in In-Situ measurements technologies. We were the first to measure in this manner using spectroscopy. In-situ measurements eliminate any need for sample handling and conditioning. In addition, the only thing leaving the stack is a signal and the resulting measurement is an average of any/all concentration gradients in the line of sight of the analyzer. Today, these sensors are still state-of-the-art technology for single gas measurements in combustion control and emissions monitoring applications.