public double timeSpanInMinutes(DateTimeStamp dateTimeStamp) {
        return this.minus(dateTimeStamp) / 60.0d;
    }
@Test
    void timeSpanInMinutes() {
        DateTimeStamp a = new DateTimeStamp(.586);
        DateTimeStamp b = new DateTimeStamp(.587);
        double diff = b.timeSpanInMinutes(a);
        assertEquals( 0.001d / 60.0d, diff, .001);

        a = new DateTimeStamp("2018-04-04T09:10:00.586-0100");
        b = new DateTimeStamp("2018-04-04T09:10:00.587-0100");
        diff = b.timeSpanInMinutes(a);
        assertEquals(0.001d / 60.0d, diff, .001);

        a = new DateTimeStamp("2018-04-04T09:10:00.586-0100", .18);
        b = new DateTimeStamp("2018-04-04T09:10:00.587-0100", .19);
        diff = b.timeSpanInMinutes(a);
        assertEquals((0.19d - 0.18d) / 60d, diff, .001);
    }