"Ruler Pad" makes you iPad be a ruler.
This is the ruler of the sub-metric and imperial measurements are displayed.
It contains two designated blocks. It can calculate the distance between the two designated blocks.
You can put small object into the test on ipad. Move the blocks. Align blocks to both ends of the object. The distance between the two blocks is designated the length of the object.
Ruler Pad for iPad on the iTunes App Store