Glucose Adjustments¶

Glucose Adjustments can change or smooth the values shown by xDrip4iOS. The original readings remain stored.

Select Glucose Adjustments in the toolbar at the top of Home. Choose the number of hours shown in the preview chart before changing the settings.

Adjustment¶

Glucose Adjustment is intended for sensors and follower sources that cannot be calibrated directly.

It is different from sensor calibration. Calibration changes how the sensor or xDrip algorithm calculates glucose. Adjustment changes the completed glucose value afterwards.

If the active sensor already has a suitable calibration process, xDrip4iOS disables Adjustment. This prevents two different correction systems from being applied to the same glucose values.

Adjustment is available for glucose sources where direct calibration is not available. This includes compatible factory-calibrated sensors and follower data sources.

Add BG checks first¶

Before creating an adjustment, add recent BG checks to the chart. Ideally, use several checks from the previous 4 to 12 hours at different glucose levels:

• a lower glucose value
• a value within the normal range
• a higher glucose value

The BG checks appear as reference points in the live preview. Adjust the controls until the adjusted glucose curve follows these reference values as closely as possible.

The app does not calculate Scale or Emphasis automatically from the BG checks. The BG checks provide the real blood glucose values that you use to evaluate the live preview.

Offset¶

Offset moves the complete glucose curve up or down by the same amount.

For example, an Offset of +10 mg/dL adds 10 mg/dL to every eligible reading. An Offset of -10 mg/dL subtracts 10 mg/dL.

You can set the Offset in two ways:

• Use the plus and minus buttons to move the value up or down.
• Select the glucose value shown beside Offset and enter a current BG value. xDrip4iOS calculates the required Offset automatically.

Offset is usually sufficient when the sensor curve has the correct overall shape but remains consistently above or below the BG checks.

Scale¶

Some sensors produce a glucose curve that appears flatter or more exaggerated than the BG checks.

Scale changes the distance between lower and higher glucose values:

• 1.00 keeps the original range.
• A Scale below 1.00 pulls the curve inwards and reduces the difference between lower and higher values.
• A Scale above 1.00 stretches the curve outwards and increases the difference between lower and higher values.

For example, with Normal Emphasis and no Offset:

Original	Scale 0.90	Scale 1.10
70 mg/dL	73 mg/dL	67 mg/dL
100 mg/dL	100 mg/dL	100 mg/dL
200 mg/dL	190 mg/dL	210 mg/dL

Use several BG checks at different glucose levels when changing Scale. The app warns when there are not enough BG checks visible in the preview.

Adjust Scale until the difference between the lower, in-range and higher parts of the curve matches the BG checks more closely.

Emphasis¶

Emphasis changes which part of the glucose range is affected most by Scale.

• Normal applies Scale around the middle of the glucose range.
• Highs biases the Scale effect towards higher glucose values.
• Lows biases the Scale effect towards lower glucose values.

Emphasis does not make a separate adjustment. It changes the centre around which Scale stretches or compresses the curve.

Emphasis has no effect when Scale is 1.00.

Suggested workflow¶

1. Select a preview period containing several useful BG checks. Normally, use the previous 4 to 12 hours.
2. Enable Adjustment.
3. Set the Offset so the curve is generally aligned with the BG checks.
4. Compare the lower, in-range and higher parts of the curve.
5. If the curve is too flat or too exaggerated, adjust Scale.
6. If the Scale correction is needed mainly at higher or lower values, change Emphasis.
7. Continue adjusting Offset and Scale while watching the live preview.
8. Apply from Now first, or apply to the selected historical period when you are satisfied with the preview.

It can take some practice to balance Offset, Scale and Emphasis. The live preview allows you to see the combined result before applying it.

Smoothing¶

Enable Smoothing, then select Light, Medium, or Strong. Select an Algorithm:

• Savitzky-Golay is the default. It smooths short sections while keeping the general shape of peaks and troughs.
• Exponential calms recent changes with less flattening.
• Kalman produces a steadier curve with more visible filtering.
• LOESS follows ramps and bends with a less rigid curve.
• Hampel + Savitzky-Golay first reduces isolated spikes, then smooths the wider curve.

Preview the result before applying it.

Smoothing can hide a real rapid change or make the chart appear delayed.

Reading frequency¶

Some sources provide readings more often than every five minutes. When Reading Frequency is shown, enable 5-minute readings to use one visible reading approximately every five minutes. Nightscout and Apple Health have separate options for storing the extra readings.

Apply the changes¶

Under Apply From, select Now or an available period of recent history, then select Apply. Applying to a previous period replaces the displayed values for that period. Read any message below the selection because it states whether Nightscout or Dexcom Share data will also be updated.

Original readings¶

Enable Original Values under Settings > General > Home Screen to compare them with the adjusted readings. You can also compare both values in Glucose Readings.

When adjustments are active, press and hold the Glucose Adjustments button on Home to show the original readings temporarily.