Movable computer ruler (MCR): a new method for measuring the size of Toxoplasma gondii cysts, tachyzoites and other selected parasites.

A new method for measuring the size of parasites and other objects using optical microscopy was developed using a specifically designed movable computer ruler (MCR) derived from digital images of a stage micrometer. Subsequently, MCR can be superimposed on images of parasites to measure their size. MCR derived from the stage micrometer under a particular objective lens can be used to measure the size of an object acquired by the same lens/microscope/camera system. The conditions are fixed for every superimposed image including width, height, pixel number and density. The MCR was tested using selected parasites, and shown to be as accurate as the ocular micrometer disk, screw micrometer eyepiece and image analysis software. The lower technical complexity of the MCR method makes it applicable even in laboratories with limited resources.