You could use a simple volt-ohm meter (VOM). You can purchase one at Radio Shack, or just borrow one from someone. These devices usually only come with small metal probes which probably doesn't tell you very accurately your body's resistance when using a zapper because of the large handholds that we use with such devices. If you have a zapper, put the zapper handhold devices (i.e., 3/4 inch copper pipes) in your hands with saltwater wetted paper towels inbetween the handholds and your skin. But instead of plugging the handholds into the zapper, connect each lead with the VOM probes. Your VOM needs to be set at the resistance setting (ohms), and measure the resistance. The reading should be somewhere between 500 ohms and 50,000 ohms. You may need to adjust the resistance range of the VOM so that the resistance measured will fall within the range of the VOM at its setting.