diff --git a/STATUS.md b/STATUS.md
index c3e2f405..cb62be7f 100644
--- a/STATUS.md
+++ b/STATUS.md
@@ -235,7 +235,7 @@ Floating point mathematical routines - not official, but well known and broadly
 | `$BC0F`   | `mov_FAC1_FAC2`        | DONE     | From the Microsoft BASIC, original name: MOVEF     |
 | `$BC1B`   | `round_FAC1`           | PARTIAL  | not fully tested yet                               |
 | `$BC2B`   | `sgn_FAC1_A`           | DONE     | From the Microsoft BASIC, original name: SIGN      |
-| `$BC39`   | `sgn_FAC1`             | DONE     |                                                    |
+| `$BC39`   | `sgn_FAC1`             | DONE     | From the Microsoft BASIC, original name: SGN       |
 | `$BC3C`   | `convert_A_to_FAC1`    | DONE     |                                                    |
 | `$BC44`   | `convert_i16_to_FAC1`  | DONE     |                                                    |
 | `$BC58`   | `abs_FAC1`             | DONE     | From the Microsoft BASIC, original name: ABS       |
diff --git a/src/basic/math/bc39.sgn_FAC1.s b/src/basic/math/bc39.sgn_FAC1.s
index 20be7ef3..f3dcad7c 100644
--- a/src/basic/math/bc39.sgn_FAC1.s
+++ b/src/basic/math/bc39.sgn_FAC1.s
@@ -3,12 +3,16 @@
 ;; #LAYOUT# *   BASIC_0 #TAKE
 ;; #LAYOUT# *   *       #IGNORE
 
-;
+; This file is under the MIT license, it contains code released by Microsoft Corporation.
+; See LICENSE for more information.
+
 ; Math package - evaluate FAC1 sign, to FAC1
 ;
 ; Output:
 ; - FAC1 - 0 for FAC1 equal 0, 1 for FAC1 > 0, -1 for FAC1 < 0
 ;
+; This is verified to be identical to the original Microsoft implementation where it was named SGN.
+;
 ; See also:
 ; - [CM64] Computes Mapping the Commodore 64 - page 115
 ; - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
@@ -17,4 +21,5 @@
 
 sgn_FAC1:
 	jsr sgn_FAC1_A
+
 	; Fallthrough to convert_A_to_FAC1
diff --git a/tools/similarity.c b/tools/similarity.c
index 4a5d20db..a27c7375 100644
--- a/tools/similarity.c
+++ b/tools/similarity.c
@@ -28,7 +28,7 @@ unsigned short microsoft_basic_chunks[NUM_CHUNKS * 2] = {
     0xB947, 0xB97D,
     0xB983, 0xB9BB,
     0xBBA2, 0xBC1A,
-    0xBC2B, 0xBC38,
+    0xBC2B, 0xBC3B,
     0xBC58, 0xBC5A,
     0xBC9B, 0xBCF2,
 };