The Ermenrich NetGeeks NU25 is an optical multimeter that offers many measurement capabilities for fiber optic networks. Its main functions include:

• Built-in, non-removable 3.7V lithium battery.
• Auto power-off function after 30 minutes of inactivity to save energy.
• Six hours of battery life on a full charge.
• Optical power measurement in the range from −60 to +8dBm.
• Supports FC/SC/ST type optical connections and RJ45 networks.
• Three additional functions: frequency detector, QC cable crystal check, and VFL (Visual Fault Locator).

The VFL function allows damage assessment in cables using light signals, with three signal types: continuous light, slow flashing, and fast flashing. Network test results are displayed on a TFT screen with backlight, including connector crimping quality tests and detected signal frequency. The device's connector is protected from dust and water with a removable plastic cover.

The device can operate at one of six main frequencies: 850, 980, 1310, 1490, 1550, or 1625nm. The VFL function features a separate wavelength of 650nm and detectable frequencies of 270Hz, 1kHz, and 2kHz. The Ermenrich NetGeeks NU25 supports single-mode (SM) and multi-mode (MM) cables.