code: function calculate_expected_delta(target_bg, eventual_bg, bgi) {
      // (hours * mins_per_hour) / 5 = how many 5 minute periods in 2h = 24
      var five_min_blocks = (2 * 60) / 5;
      var target_delta = target_bg - eventual_bg;
      var expectedDelta = round(bgi + (target_delta / five_min_blocks), 1);
      return expectedDelta;
  }
docs: we expect BG to rise or fall at the rate of BGI, adjusted by the rate at which BG would need to rise / fall to get eventualBG to target over 2 hours