diff --git a/src/basic/math/b91d.NORM2.s b/src/basic/math/b91d.NORM2.s
new file mode 100644
index 00000000..2f6c3ff8
--- /dev/null
+++ b/src/basic/math/b91d.NORM2.s
@@ -0,0 +1,35 @@
+;; #LAYOUT# STD *       #TAKE
+;; #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
+;; #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 - continuation of normalize FAC1 function
+;
+; This is verified to be identical to the original Microsoft implementation where it was named NORM2.
+;
+; See also:
+; - [CM64] Computes Mapping the Commodore 64 - page 113
+; - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
+; - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
+;
+
+NORM2:
+    adc #1              ; Decrement shift count
+    asl FACOV           ; Shift all left one bit
+    rol FAC1_mantissa+3
+    rol FAC1_mantissa+2
+    rol FAC1_mantissa+1
+    rol FAC1_mantissa+0
+NORM1:
+    bpl NORM2           ; If MSB=0 shift again
+    sec
+    sbc FAC1_exponent
+    bcs zero_FAC1
+    eor #$FF
+    adc #1              ; Complement
+    sta FAC1_exponent
+    
+    ; Fallthrough to shift_carry_into_FAC1
diff --git a/tools/similarity.c b/tools/similarity.c
index d2b3d10a..4950143f 100644
--- a/tools/similarity.c
+++ b/tools/similarity.c
@@ -20,13 +20,14 @@ int matches[MAX_SIZE];
 
 int phase_mask[MAX_SIZE+MAX_SIZE];
 
-#define NUM_CHUNKS 9
+#define NUM_CHUNKS 10
 // Pairs of start, end memory addresses of known exact similarity with the open source Microsoft BASIC
 unsigned short microsoft_basic_chunks[NUM_CHUNKS * 2] = {
     0xB391, 0xB39D,
     0xB3A2, 0xB3A5,
     0xB849, 0xB869,
     0xB8D2, 0xB8FD,
+    0xB91D, 0xB935,
     0xB947, 0xB97D,
     0xB983, 0xB9BB,
     0xBA8C, 0xBAB6,