The mini Secchi disk is a small, circular disk that is used to measure the transparency of water. The Secchi disk is named after its inventor, an Italian astronomer named Angelo Secchi, who developed the tool in the 19th century. To use a mini Secchi disk, a person simply lowers the disk into the water until it is no longer visible, and then measures the depth at which the disk disappears. This measurement can be used to estimate the transparency of the water, which can be an indication of its quality.