in src/scaleDetector.ts [33:42]
constructor(svgElement: Selection<SVGRectElement, any, any, any>) {
this.scaleDetectorElement = <SVGRectElement>svgElement
.append("rect") // Using a <rect> which should have a reliable bounding box across browser implementations.
.classed("scale-detector", true)
.attr("width", 1)
.attr("height", 1)
.attr("stroke-width", "0px")
.attr("fill", "none")
.node();
}