Designed in line with digitalization concept, the portable test kit “TWIN CHECK” enables regular on-site measurements of two critical parameters of lubricating and hydraulic oil: water concentration in oil and base number (BN). Water represents substantial threat to any mineral oil application and base number shows the degree of oil protection against deposit formations and possible corrosive wear of the engine system. Early detection of any changes in the oil condition (i.e., water contamination) or degradation of the oil quality (when BN is too low or too high) helps to take responsive corrective actions at the exact time when they are required in order to ensure effective functioning of machinery. Water concentration in oil and BN of the used lubricant are measured similarly employing the digital test device “TWIN CHECK” with integrated microprocessor and pressure sensor and special chemical reagents. Total measuring time can vary from 2 minutes up to max. 20 minutes and is directly dependant on the exact amount of water contained in the oil sample/ BN value. The digital test device facilitates massively the testing process and delivers quick and precise digital test results. It is offered in modular design with interchangeable components (plugged or screwed) to allow cost-effective maintenance and easy repair directly on board a vessel. An internal memory chip of large capacity and USB to serial connection allow data recording and transfer for trend analysis.