The Peak LCR tester will not measure produce an ESR measurement and in-circuit measurements are not recommended. You will need to discharge capacitors prior to testing like most LCR meters. It will test capacitance, inductance, and resistance at a few different frequencies. If you are looking for a decent unit that can measure capacitance and ESR, my vote would go to the Peak Atlas ESR70. The unit discharges caps up to 50V, does in-circuit measurements, and you can use different test probes (alligator, hooks, probes, etc.). I also have the inexpensive MESR100v2 that does a good job with reading ESR but that it. The leads are short, you need to discharge caps before testing, and no capacitance measurements.