PLJ 8LED H RF Frequency Counter Cymometer Tester Module 0.1 to 1000MHz (Backlit font blue)

I received an incredible electronic device from the seller. This was a frequency counter that has a very nice LED seven segment display; and in its advertised frequency range can measure - for example, a 4 MHz signal with acurracy to 1 Hz. My student used this device to measure the frequency of a Colpitts 4 MHz quartz crystal oscillator vs. the capacitance of a capacitor that was in series with the quartz crystal. Since we could measure 1 Hz variationss in the crystal oscillator, the student could make a plot of frequency vs. capacitance using capacitors from a range of several pico Farads to 30 pico Farads and obtain a very smooth curve. From this curve one could determine a few of the important parameters that model the quartz crystal in its fundamental mode of oscillation. Just apply 12 volts DC, input a clock type of signal and you are all set. I recommend this instrument vs. purchasing a commercial grade frequency counter if your want an economical solution to measuring frequency.