This self-contained, computerized diagnostics system examines control valve performance in order to improve productivity and product quality in process control. By measuring critical aspects of control valve performance, the system identifies valve assemblies that deviate from optimum accuracy, speed of response or overshoot. Valves can be in-line or bench tested. Pentium computers with 16 MB RAM, monitor and signal conditioners are all protected in an industrial case. The valve diagnostics system can be purchased, leased, or provided as a service by trained DZ technicians. DZ personnel are available to provide diagnostic testing or conduct in-plant training.