diff --git a/STATUS.md b/STATUS.md
index 53bab291..408f61ae 100644
--- a/STATUS.md
+++ b/STATUS.md
@@ -253,8 +253,8 @@ Floating point mathematical routines - not official, but well known and broadly
 | `$E097`   | `rnd_FAC1`             | DONE     |                                                    |
 | `$E09A`   | `rnd_A`                | DONE     |                                                    |
 | `$E0BE`   | `rnd_generate`         | DONE     |                                                    |
-| `$E264`   | `cos_FAC1`             | PARTIAL  | needs `sin_FAC1`                                   |
-| `$E26B`   | `sin_FAC1`             | NOT DONE | some work already started                          |
+| `$E264`   | `cos_FAC1`             | PARTIAL  | not fully tested yet                               |
+| `$E26B`   | `sin_FAC1`             | PARTIAL  | not fully tested yet                               |
 | `$E2B4`   | `tan_FAC1`             | NOT DONE |                                                    |
 | `$E30E`   | `atn_FAC1`             | NOT DONE |                                                    |
 
diff --git a/src/basic/,stubs_math/e26b.sin_FAC1.s b/src/basic/,stubs_math/e26b.sin_FAC1.s
deleted file mode 100644
index f1f2f340..00000000
--- a/src/basic/,stubs_math/e26b.sin_FAC1.s
+++ /dev/null
@@ -1,29 +0,0 @@
-;; #LAYOUT# STD *       #TAKE
-;; #LAYOUT# *   BASIC_0 #TAKE
-;; #LAYOUT# *   *       #IGNORE
-
-;
-; Math package - sine of FAC1 in radians
-;
-; See also:
-; - [CM64] Computes Mapping the Commodore 64 - page 210 - XXX address does not match
-; - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
-; - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
-;
-
-; XXX provide implementation
-
-sin_FAC1:
-
-	+STUB_IMPLEMENTATION
-
-poly_sin:
-
-	!byte $05                          ; series length - 1
-
-	+PUT_CONST_POLY_SIN_1
-	+PUT_CONST_POLY_SIN_2
-	+PUT_CONST_POLY_SIN_3
-	+PUT_CONST_POLY_SIN_4
-	+PUT_CONST_POLY_SIN_5
-	+PUT_CONST_POLY_SIN_6
diff --git a/src/basic/,stubs_math/e26b.interop b/src/basic/math/e26b.interop
similarity index 100%
rename from src/basic/,stubs_math/e26b.interop
rename to src/basic/math/e26b.interop
diff --git a/src/basic/math/e26b.sin_FAC1.s b/src/basic/math/e26b.sin_FAC1.s
new file mode 100644
index 00000000..65c48f0f
--- /dev/null
+++ b/src/basic/math/e26b.sin_FAC1.s
@@ -0,0 +1,55 @@
+;; #LAYOUT# STD *       #TAKE
+;; #LAYOUT# *   BASIC_0 #TAKE
+;; #LAYOUT# *   *       #IGNORE
+
+;
+; Math package - sine of FAC1 in radians
+;
+; See also:
+; - [CM64] Computes Mapping the Commodore 64 - page 210 - XXX address does not match
+; - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
+; - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
+; - https://www.c64-wiki.com/wiki/SIN
+
+
+
+sin_FAC1:
+
+    jsr mov_FAC1_FAC2               ; FAC1 <- X / (2*pi)     (X2)
+    ldy #>const_DOUBLE_PI
+    lda #<const_DOUBLE_PI
+    jsr mov_MEM_FAC1
+    jsr div_FAC2_FAC1
+
+    jsr mov_FAC1_FAC2               ; FAC2 <- X2
+    jsr int_FAC1                    ; FAC1 <- INT(X2)
+    jsr sub_FAC2_FAC1               ; FAC1 <- X2 - INT(X2)   (F)
+
+    ldy #>const_QUARTER
+    lda #<const_QUARTER
+    jsr FCOMP
+    bmi sin_next                    ; FAC1 < 0.25
+
+    ldy #>sin_three_quarters
+    lda #<sin_three_quarters
+    jsr FCOMP
+    bmi sin_q23                     ; FAC1 < 0.75
+
+    jsr mov_FAC1_FAC2               ; FAC1 <- FAC1 - 1.0
+    ldy #>const_ONE
+    lda #<const_ONE
+    jsr mov_MEM_FAC1
+    jsr sub_FAC2_FAC1
+    +bra sin_next
+
+sin_q23:
+    ldy #>const_HALF
+    lda #<const_HALF
+    jsr sub_MEM_FAC1                ; FAC1 <- 0.5 - FAC1
+
+    ; FALLTHROUGH
+    
+sin_next:
+    ldy #>poly_sin
+    lda #<poly_sin
+    jmp poly1_FAC1
diff --git a/src/basic/math/poly_sin.s b/src/basic/math/poly_sin.s
new file mode 100644
index 00000000..1f37c2e6
--- /dev/null
+++ b/src/basic/math/poly_sin.s
@@ -0,0 +1,23 @@
+;; #LAYOUT# STD *       #TAKE
+;; #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
+;; #LAYOUT# *  BASIC_0  #TAKE
+;; #LAYOUT# *   *       #IGNORE
+
+; Polynomial for the sine function
+
+
+poly_sin:
+
+	!byte $05                          ; series length - 1
+
+	+PUT_CONST_POLY_SIN_1
+	+PUT_CONST_POLY_SIN_2
+	+PUT_CONST_POLY_SIN_3
+	+PUT_CONST_POLY_SIN_4
+	+PUT_CONST_POLY_SIN_5
+	+PUT_CONST_POLY_SIN_6
+
+	
+; Constant 0.75 needed for sine calculation
+sin_three_quarters:
+    !byte $80, $40, $00, $00, $00
diff --git a/strings/85248425A0 b/strings/85248425A0
new file mode 100644
index 00000000..86536202
--- /dev/null
+++ b/strings/85248425A0
@@ -0,0 +1,3 @@
+STA $24 + STY $25 + LDY fragment
+
+Store YA to well known vector address in the zero page