This digital multimeter is useful for evaluating textiles and thread for conductivity and electrical resistance.
Because each colored led have a different forward voltage different “scales are provided”, Blue is good for low resistance, Green for middle, and red for higher resistance.
It is is easily built by soldering the anode or cathode of the RGB led (the longest lead) to the appropriate battery terminal.
The other leads are twisted with round nosed jewelry pliers into spirals.
To use it simply insert the material to be tested between the spiral LED lead and the battery top and press with one of your "digits" to translate conductivity into LED current and brightness.