negative values in circumference should be banned

[ebarry]

The otherwise nice scrolling feature on numerical entry fields easy allows for erroneously entering negative values, for instance on circumference and distance, which should never be negative.

Negative values in circumference were not flagged even upon Submit.

Can negative values be blocked?

[ebarry]

Negative values are allowed for distance, length, width, circumference.

But it's the negative length that causes a bigger error -- see treebed second from left where a negative length flipped it onto the wrong side of the street and twisted it: