In this paper we propose and develop a complete solution to measure very low tunneling currents in Non-Volatile Memories, based on the Floating-Gate technique. We aim at using very basic tools (power supply, multimeter...) but still having a very good current resolution. The key node of our solution is that the experiment is led in a very particular low-noise environment (underground laboratory) allowing to keep the electrical contacts on the device under test as long as possible. The aim of this work is to show both the feasibility of such measurements and the ability to reach current levels lower than the ones obtained by any direct measurement, even from high-performance devices such as HP4156 or Keysight B1500 with atto-sense and switch unit (ASU). We have obtained the complete I-V characteristics of tunnel oxide with a very promising 10(-17) A current level, two decades lower than any direct measurement.