Battery not included
1.5V battery (LR44)
Digital confusion – There are three main reasons:
A. The surface of the protective film is damp or stained with cutting fluid (or other conductive particles).
Treatment: Wipe the surface of the ruler and the protective film with a dry cloth slightly dampened with absolute ethanol or aviation gasoline. Gently twist a small drop of absolute ethanol or aviation gasoline (be careful not to drip too much, otherwise the liquid will enter the electronic components causing other problems!)
B. The copper-clad plate under the protective film is affected by corrosion and blackening.
Treatment method: Uncover the protective film, polish the surface of the copper strip with high-grade rubber or metallographic sandpaper, and clean it.
C, The battery is not enough – treatment: replace a new battery.