Abstract: A turbidimeter includes a housing having a cavity with an inlet through which the fluid enters the bottom of the cavity, and an outlet through which the fluid exits the top of the cavity. A removable baffle assembly is located within the cavity between the inlet and outlet. The baffle assembly is formed by three vertical plates spaced from each other and extending across substantially the entire cross sectional area of the cavity. The first plate defines a first passage near the top of the cavity through which all the fluid entering the cavity must flow. The second and third walls define a second passage near the top of the cavity through which gas bubbles entrained in the fluid travels to the outlet. A third passage is defined between the first wall and the outlet and a mechanism is provided for measuring the turbidity of the fluid flowing through the third passage. A calibration device formed by a block of glass ceramic material is insertable in the third passage to simulate a known turbidity fluid.