This ruler has three main features aimed at aiding in the drawing of graphs: 

• dashed line ruler: usefull for drawing aysmptotes quickly and neatly 
• Indented ruler: allows for the consistent spacing of tick marks (3mm & 5mm depending on the version) 
• small size: makes it much less cumbersome to use than a full or even min size ruler

there are two sizes of this ruler, a 3mm & 5mm. the sizing refers to the length of the dashes and the space between indents it should be noted that the 5mm ruler is a tad bit larger than the 3mm. 

which one should I choose: I prefer the 3mm ruler as it produces smaller graphs but the 5mm size is a more forgiving print and works well with a 0.6mm nozzel.

how do I used the dash line part: Line up your pencil with one of the two inner sides of the ruler pressing lightly against the inner side and swipe it forwards. Please note that the action will get better over time as the pencil will slowly fill in any rough patches with graphite. 

Recommended print seting: use as low a layer hight as allowed for your nozzle as it will produce smother dashed line drawing experience, other than that default setting are fine.