The mini tools button is located in the toolbar at the bottom. Once you select it, a menu unfolds and you can choose your desired mini tool. The mini tool is then placed on the page directly.
Mini tools are tools that are stuck to a page. They will therefore appear on every page of your Presenter file and also when expanding, moving or shifting the work field on the same page. This way you can easily and instantly use the tool without the need to search for it.
After placing the ruler on the canvas you can draw straight lines along the top of the mini tool. Select the pencil to change the colour of the line.