A compact and lightweight self-recording pressure based sea level gauge has been designed to suit deployments from harbour and offshore environments. A novel hydraulic coupling device designed in-house was used to transfer the seawater pressure to the pressure transducer. This paper discussed the mechanical and electronic design of the instrument, calibration results, field-performance, and validation. The instrument was calibrated using an in-house facility and validation tests performed at Zuari Estuary, Goa, India against a conventional analog-type float-driven sea level gauge, and a digital-type float-driven sea level gauge. All the three devices exhibited similar trends in their responses. The observed minor differences can be attributed to corresponding differences in the responses of these devices to changing site-specific environmental factors such as currents, waves, estuarine water density variations with changing phases of the tide, and so forth. The monthly-mean sea levels derived from the SOI and the NIO gauges were closer within approx 1.5 mm.