Analysis can draw marks and rulers. The difference is that rulers are only drawn in one dimension (horizontal or vertical) where as marks are drawn in all dimensions. When you draw a mark or ruler in one window, it is automatically also drawn in all other windows. This is a very useful way of checking whether peaks are really at the same height or not. To draw a ruler press h or v for horizontal and vertical rulers, respectively, and it will be drawn at the current mouse position. To draw a mark, press m. n will remove all marks and rulers. You can also draw marks and rulers using the Marker menu in your Right Click mouse menu. This also allows you to remove only marks or only rulers rather than all at the same time. By default only one mark and ruler can be drawn at any one time (i.e. if you draw a second, the first goes away). To increase the number you can draw, go to the Windows menu and select Marks and Rulers. Here you can also select the colour of your marks and rulers. Marks have the added feature that if you draw them near to a peak, they will automatically position themselves on the peak and be black. Otherwise they will go at the precise mouse position and be the colour selected in the Marks and Rulers pop-up.