Sumit Enterprises

A soil hydrometer is a laboratory instrument used in soil mechanics to determine the particle size distribution of fine-grained soils, specifically those finer than 0.075 mm (75 μm) in diameter. It measures the density of a soil suspension over time to estimate the proportions of different particle sizes (silt and clay). 

A thermo hygrometer is designed to be able to measure both air temperature and humidity. The temperature is typically measured with a digital thermometer. There may be a sensor attached to the device itself or it may have an additional sensor that can be placed in a position that's remote from the main unit.