Relay in DIY LC Meter

[Kimly]

What is the function of the relay in the DIY L/C meter link below?

Accurate L/C Meter

[Jerome Trent]

     SW2 switches between measuring an inductor (L) or measuring a capacitor (C). In the L position the inductor being measured is connected in series with the 82uH inductor, and it’s other end is connected to ground. This places these two series inductors in parallel with Ccal capacitor which is a known capacitor value. Now the microcontroller can calculate the inductor value based on the resonant frequency formula since we have a known capacitor value and a known frequency.

      The circuit is auto-ranging and can measure a wide range of inductor values. For larger inductor values, pin 18 of the microcontroller would go low causing the reed relay to close. This would place another know capacitor value in parallel with Ccal. Since they are in parallel they add to provide 2000pF to use in testing the unknown inductor. So the relay is a part of the auto-ranging circuitry.