Help for a TOTAL NEWBIE - Scale/Ruler plugin ?

Best approach would be to take some of the Krpano examples and play with it.
In this case, you should create your own buttons or add new buttons next to krpano default icons.

Defining new icon - adapted default skin xml

<plugin name="rulers"  	align="bottom" x="+100" y="10" style="button" crop="440|0|40|40" onovercrop="440|40|40|40" ondowncrop="440|80|40|40" onhover="action(calculatesize); set(plugin[openimage].visible, true);" onout="set(plugin[openimage].visible, false);"/>

is croping new icon that is added to buttons.png and display it on correct place with onover and ondown crop icon definition.

Ruller is actualy transparent PNG that is used to create plugin which is turned on (visible="true") when mouse is onhover button "ruller"
Than calulatesize code is called. I would suggest you to contact the owner of this code and ask if he will allow you to use his part of code. I see lot of calculations done there and would assume lot of coding hours went in that direction to develop this "plugin"

That would be basic. As I sad, take example and play with it and come here for help if you are stucked. Provide link to your code, that would help a lot to take a look and provide you with giudelines.
regards