Review on Tekpower TP4000ZC Auto Ranging DMM with USB Interface - PC Based Digital Multimeter, Similar to MS8220R, Computer Compatible by Timothy Schroeder

I bought this specifically for the RS232 interface as I needed to do long term data logging for a project. The included software worked in XP but didn't work properly on my Win7 x64 machine - I'm a computer engineer with 35 years of experience writing software, so I know how to work around all Windows compatibility issues and have tried everything before you give up. To counter this, I deployed Visual Studio and wrote my own data logger. The meter was flawless and for the price and functionality you couldn't beat it. I really needed an extra serial port, so I grabbed a cheap USB-to-serial dongle from Trendnet. The counter has a very long battery life. No complaints on that front. Sensors are cheap, but I've used other sensors since I got the meter.