Placing blocks can be quite a delicate tasks sometimes when the position of the blocks depends on other entities in the drawing. With the 'Measure Dynamic' command the position of the blocks can be carefully considered and aimed. By moving your cursor circles will move along and change position. They will stay on the selected linear entity however, as the measure command does. Once you click the position is fixed and the circles are turned into blocks. To make it easier for your computer the command by default draws circles as placeholders for the blocks. You can adjust the radius of the circle but you can also decide to have the blocks placed straight away with the Place option. Like AutoCAD's native measure command you can set the distance and whether the blocks should be aligned. While placing the blocks the starting distance shows live in the command line. By typing an S you can specify a starting distance which will fix the position of the blocks matching that starting position. By default the blocks are grouped so when you select one block you select them all.