Inconsistent return values from Google Maps geometry calculations

Question

I am developing an application using Google Maps. I have some logic which expects very consistent output form the google.maps.geometry.spherical library.

Basically I am trying to draw a box with precise dimensions.

My sample code looks like this:

function (LatLng) {

  var NW, NE, SW, SE, length, dist; 

  // LatLng is a coordinate
  NW = LatLng

  // I have a length variable
  length = 25

  // Using the single reference point as NorthWest corner of the box, 
  // I calculate the remaining 3 corners
  NE = google.maps.geometry.spherical.computeOffset(LatLng, length, 90);
  SW = google.maps.geometry.spherical.computeOffset(LatLng, length, 180);
  SE = google.maps.geometry.spherical.computeOffset(SW, length, 90);

  // now I check the dimensions
  dist = google.maps.geometry.spherical.computeDistanceBetween(NE, NW);

  console.log('NW/NE bounds distance', dist);
}

I am expecting to get a value of 25 (equal to length), and indeed my subsequent logic depends on dist >= length. However, when I run this multiple times I get some degree of variability around 25. I find anything from range 22.499999999193243 to 22.50000000221681 for example.

Is this variability to be expected? Is this a feature of the developer API?

If so, does anyone have suggestions on how to account for this in my code, as simply adding 0.000000001 to the dimensions seems a bit fudgey to me.

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P.S.

This is a simplified version of my problem. In the real code I am actually generating a Rectangle object, then calculating the distances between corners to compare to length. However the principal, and error, is exactly the same.