Process monitoring test instruments evaluate, maintain, create, and calibrate process systems in order to increase efficiency and identify problems before they cause downtime. When relative change is a significant aspect in a process, analog panel meters are often used. They have a moving needle and a numbered dial that shows temperature, speed, pressure, and current measurements. Digital panel meters detect electrical flow conditions like voltage and current with precision and display the results on an easy-to-read LCD or LED screen. Process calibrators, process loop calibrators, and temperature calibrators are portable, handheld instruments used to calibrate and measure values in instrumentation in order to detect defects in process applications. Ultrasonic flow meters detect and measure the speed of liquid or gas inside a pipe using ultrasonic waves.