The Marquette Dyna-Chek Model 41-109 is a vintage automotive test meter used for troubleshooting electrical problems. It is an ammeter-ohmmeter and alternator-diode tester, which is a type of electrical measuring instrument that can measure voltage, current, and resistance. The device was manufactured by Marquette, which also produced other vintage automotive test equipment like the Marquette AVR Tester Model 41-135 and the Marquette Porta-Tuner Engine Analyzer Model T-200.