Tape Measure is an item added by Bibliocraft. The Tape Measure can measure a distance given from one block to another.
In absolute measurement mode, right-clicking on a block selects a block, then right-clicking on any other block will give the distance between those blocks to the nearest meter. This works across angles, but will be slightly less accurate. Right-clicking the Tape Measure with no block selected will change to individual measurement mode, which will return separate measurements, in blocks/meters for each direction, north/south, east/west, and height. Dimensions are only returned if the measured distance is greater than 0.
Tape Measures can be used to rotate items on the Table by right clicking on any of the 4 sides of the table.