Instrumentation can be broadly defined as any physical tool or device used to obtain data or monitor a process's performance. The measured variable is the term used to describe any variable monitored or measured during an experiment. It can be anything from temperature to pressure to concentration. It is essential to keep track of these measurements to ensure that the experiment is proceeding as planned and that the results are accurate. You can do this through data acquisition systems or software programs, which you can use to analyze the data and produce corresponding results.