diff --git a/firmware/hw_layer/sensors/CJ125.h b/firmware/hw_layer/sensors/CJ125.h
index 194b73881b..3f858691cf 100644
--- a/firmware/hw_layer/sensors/CJ125.h
+++ b/firmware/hw_layer/sensors/CJ125.h
@@ -16,6 +16,32 @@
 #define	DIAG_REG_RD						0x78 // Read Diagnostics Register
 #define	INIT_REG2_RD					0x7E // Read Initialization Register 2
 
+/**********************************************************************************
+    INIT_REG1 - CJ125 Initialization Register 1
+        00x000x0
+        ||||||||---- VL - Pump Current Sense Amplifier - 0 = x8, 1 = x17
+                            If VL is set to "0" the amplification of Ip is 8.
+                            If VL is "1" the amplification is 17. The higher
+                            amplification is needed for a better resolution
+                            at Lambda > 1, amplification 8 for Lambda < 1.
+                            Note: It seems to make no difference, always set to 1.
+        |||||||----- Unused
+        ||||||------ LA - Pump Current Sense Amplifier - 0 = measurement, 1 = calibration
+                            If LA is "0" the measurement mode for Ip is active.
+                            The current pump current is displayed on Ua. If LA is
+                            set to "1" the calibration mode is active. The shown
+                            voltage on Ua must been subtracted from the later measurement.
+        |||||------- Undocumented Bit - Note: CJ125 only seems to work when set to 1.
+        ||||-------- RA - Measurement Current for Ri - 0 = measurement, 1 = calibration
+                            If RA is "0" the measurement mode for Ri is active and
+                            the current resistance of the probe is "displayed" on Ur.
+                            If RA is "1" the calibration mode is active. You get the
+                            optimal voltage for the inner resistance of the probe on Ur.
+        |||--------- Unused
+        ||---------- PA - Pump Current Control - Set to 0 to be active
+        |----------- ENABLE/HOLD - Must be set to 1 to enable
+***********************************************************************************/
+
 #define	CJ125_INIT1_NORMAL_8			0x88 // 0b10001000 (Normal mode, Amplification 8)
 #define	CJ125_INIT1_NORMAL_17			0x89 // 0b10001001 (Normal mode, Amplification 17)
 #define	CJ125_INIT1_CALBRT				0x9D // 0b10011101 (Calibration mode, LA=1, RA=1)