diff --git a/libs/serializer/src/main/java/de/cyface/serializer/LocationOffsetter.java b/libs/serializer/src/main/java/de/cyface/serializer/LocationOffsetter.java
index de749d3..e65363c 100644
--- a/libs/serializer/src/main/java/de/cyface/serializer/LocationOffsetter.java
+++ b/libs/serializer/src/main/java/de/cyface/serializer/LocationOffsetter.java
@@ -56,6 +56,9 @@ public LocationOffsetter() {
      * The first number "seen" is used as offset and returned as absolute number. Subsequent numbers are returned in the
      * diff-format, i.e. as the relative difference to the previous number passed.
      *
+     * TODO: When we support nullable elevations, we need to ensure we implement it the same as communicated in STAD-827.
+     * - 100, 101, null, 200, 201, null, null → 100, +1, null, 200, +1, null, null
+     *
      * @param location the data point to be converted.
      * @return the data point in the offset-format
      */
diff --git a/libs/serializer/src/main/java/de/cyface/serializer/LocationSerializer.java b/libs/serializer/src/main/java/de/cyface/serializer/LocationSerializer.java
index ac8d27a..3040629 100644
--- a/libs/serializer/src/main/java/de/cyface/serializer/LocationSerializer.java
+++ b/libs/serializer/src/main/java/de/cyface/serializer/LocationSerializer.java
@@ -51,6 +51,8 @@ public static de.cyface.protos.model.LocationRecords locations(final List<RawRec
                     l.getLongitude(), l.getSpeed(), l.getAccuracy());
             final Formatter.Location offsets = offsetter.offset(formatted);
 
+            // TODO: When we support nullable elevations, we need to ensure we implement it the same as communicated in STAD-827.
+            // - 100, 101, null, 200, 201, null, null → 100, +1, null, 200, +1, null, null
             builder.addTimestamp(offsets.getTimestamp())
                     .addLatitude(offsets.getLatitude())
                     .addLongitude(offsets.getLongitude())
diff --git a/libs/serializer/src/main/java/de/cyface/serializer/Offsetter.java b/libs/serializer/src/main/java/de/cyface/serializer/Offsetter.java
index 066f459..43e396e 100644
--- a/libs/serializer/src/main/java/de/cyface/serializer/Offsetter.java
+++ b/libs/serializer/src/main/java/de/cyface/serializer/Offsetter.java
@@ -43,6 +43,9 @@ public class Offsetter {
      * The first number "seen" is used as offset and returned as absolute number. Subsequent numbers are returned in the
      * diff-format, i.e. as the relative difference to the previous number passed.
      *
+     * TODO: When we support nullable elevations, we need to ensure we implement it the same as communicated in STAD-827.
+     * - 100, 101, null, 200, 201, null, null → 100, +1, null, 200, +1, null, null
+     *
      * @param absoluteNumber the number to be returned in the diff-format
      * @return the difference to the previous number or the absolute number for the first number.
      */