The "Test and Measurement" category includes listings for manufacturers and distributors of test and measuring instruments, whose main product line or service consists of such things as electrical calibrators, references, standards, sources, insulation resistance testers and megohmmeters, function generators, analog and digital multimeters, signal generators, pulse generators, magnetic test equipment, electro-optical measurement products, time domain reflectometers, radio test sets, speaker testers and/or spectrum analyzers. This category contains web sites of companies that sell, rent, lease or manufacture test and measurement equipment that will measure or produce an electrical quantity or signal that can be used for testing electrical or electronics equipment. These products do not measure light, fat content, chemical composition, flow rate, amount of bubbles, weight or any other quantity other than electrical.