Signal Quality. Spektrum telemetry modules keep tabs on the quality of the signal coming to the receiver and send this information back to the transmitter where it is represented on the LCD screen using a familiar signal bar scale.
A pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced sideways from its resting, equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the equilibrium position.
A pendulum is a length of chain or string with a weight on one end and just about any weight on a string or chain will work: a pendant, a wet teabag, a bead on a thread... you get the idea!. If you prefer, you can buy one online or in shops in your community.