fix intervals (#352)

src/js/utils/intervals.js

@@ -69,7 +69,15 @@ function getChartIntervals(maxValue, minValue=0) {
 	normalMaxValue = normalMaxValue.toFixed(6);
 
 	let intervals = getChartRangeIntervals(normalMaxValue, normalMinValue);
-	intervals = intervals.map(value => value * Math.pow(10, exponent));
+	intervals = intervals.map(value => {
+		// For negative exponents we want to divide by 10^-exponent to avoid
+		// floating point arithmetic bugs. For instance, in javascript
+		// 6 * 10^-1 == 0.6000000000000001, we instead want 6 / 10^1 == 0.6
+		if (exponent < 0) {
+			return value / Math.pow(10, -exponent);
+		}
+		return value * Math.pow(10, exponent);
+	});
 	return intervals;
 }