#555

Request to merge #555 into the master branch.
Using `DECIMAL/3` here is a bit obtuse.  Probably better to just use a number, rather than use a global variable that apparently isn't relevant (since you need to divide it by 3 -- a rather harsh modification).  I would think 6 should work here, which is a bit more stringent than the current test: DECIMAL/3 is 4.  

In fact, I would probably recommend going through the whole file and replacing DECIMAL by 14 where appropriate, and by a smaller number as needed.  IMO, that tends to be clearer as to how strict each test is expected to be.  e.g. anything that uses an ImageF (implicit here when you draw with no dtype or image) can't be expected to be accurate to more than about 7 decimal places.