A rectangle has 4 (straight) edges and ALL vertices (=corners) are right angled.
A square is a rectangle using all the SAME edge-lengths.
An oblong is a rectangle using 2 DIFFERENT edge-lengths.
But note they are both members of the 'rectangle family'.
This calculator is really intended to deal with oblongs, and needs 2 entries. There is a separate calculator for squares which needs only 1 entry.
Where (for brevity) it says 'edge', 'perimeter' and so on, it should, more correctly, be something like 'length of edge' or 'edge-length' etc. And the references to 'First edge' and 'Second edge' have no significance but only serve to distinguish one edge from the other.
Zero and negative numbers are not accepted as entries, and neither should they appear as solutions.
However, mathematically it is possible to have negative solutions for some of the sizes as well imaginary ones.
Such solutions are not shown here. Instead, a message is given that the two entries made do not give a REAL rectangle.