Picots are loops of thread left between the stitches in tatting. They are used for making joins as well as decoration. Lots of large picots will make the finished item more frilly looking. The picots are not counted as a stitch, they are merely the space left between stitches. Using small picots for joins will bring the elements of the design closer together.
Picots do not have to be the same size throughout your design. Try graduating the lengths to produce different looks.
You can use a picot gauge to ensure picots are the same length, especially if the pattern’s design requires it, but an easier method would be to use a permanent marker to draw a line of the correct size on your finger where you hold your work in progress. For example, if you tat right-handed and hold the completed knots between your left thumb and index finger, draw the line on your left index finger so that it lines up with the thread as you tat – from the point where your last stitch is on your finger to the end of the finished picot. If you do this method, make sure the line is twice the length of the finished picot size required because you will be measuring the “flat” picot as you make it rather than the “loop” of the picot once finished.