diff --git a/gnss/2.1/IGnssMeasurementCallback.hal b/gnss/2.1/IGnssMeasurementCallback.hal
index 60a5423..beef4fd 100644
--- a/gnss/2.1/IGnssMeasurementCallback.hal
+++ b/gnss/2.1/IGnssMeasurementCallback.hal
@@ -103,6 +103,9 @@
          *
          * The value does not include the inter-frequency Ionospheric bias.
          *
+         * The sign of the value is defined by the following equation:
+         *      corrected pseudorange = raw pseudorange - fullInterSignalBias
+         *
          * The full ISB of GnssClock.referenceSignalTypeForIsb is defined to be 0.0 nanoseconds.
          */
         double fullInterSignalBiasNs;
@@ -127,6 +130,9 @@
          * - Satellite inter-code bias (e.g., Differential Code Bias (DCB)) (with respect to the
          *   code type in GnssClock.referenceSignalTypeForIsb)
          *
+         * The sign of the value is defined by the following equation:
+         *      corrected pseudorange = raw pseudorange - satelliteInterSignalBias
+         *
          * The satellite ISB of GnssClock.referenceSignalTypeForIsb is defined to be 0.0
          * nanoseconds.
          */