Question about ruler measurements, scale and leaving multiple measurements on the image?

Hiya- I'm not sure if PS is overkill for my purposes, but I have the free trial so I figure I might as well try to figure out if it is worthwhile for what I need it for.  I'm trying to use it to measure reference photos for drawing, up until now I've just used a clear physical ruler against my laptop screen, which can add a significant amount of time as I measure and remeasure.  Ideally when I'm done I would love the image to be covered in horizontal and vertical lines that I drew across features that I can click on and it will tell me how long that line is.

-I have found the ruler tool.  Is there any way to make these lines stick so that I can have multiple measurements shown at once?

-I have figured out how to pull up the measurement log.  The default measurement on it is still in pixels even though I have changes my preferences in units and rulers to be centimeters.  I guess I'm also a bit confused about how I'm supposed to keep track of what ruler 2 measured compared to ruler 3, I was hoping that if I clicked on a line item in the measurement log that it would then show a line on the image of what that measurement was for but nothing really seems to happen.  

Thanks for any help!