diff --git a/src/libsrc/sincos.pla b/src/libsrc/sincos.pla
index 5146599e..b80d82ed 100644
--- a/src/libsrc/sincos.pla
+++ b/src/libsrc/sincos.pla
@@ -11,6 +11,7 @@ word = $C41B,$C6F3,$C9BB,$CC73,$CF1C,$D1B4,$D43C,$D6B3,$D91A,$DB6F
 word = $DDB4,$DFE7,$E209,$E419,$E617,$E804,$E9DE,$EBA6,$ED5C,$EEFF
 word = $F090,$F20E,$F378,$F4D0,$F615,$F747,$F865,$F970,$FA68,$FB4C
 word = $FC1C,$FCD9,$FD82,$FE18,$FE99,$FF07,$FF60,$FFA6,$FFD8,$FFF6
+word[2] fprounding = $8000, $0000
 
 def sin32(deg)#0
     word[2] i32
@@ -27,13 +28,13 @@ def sin32(deg)#0
         i32[0] = (sin90[180 - deg])
         i32[1] = 0
     elsif deg < 270
-        i32[0] = -(sin90[deg - 180])
+        i32[0] = ~(sin90[deg - 180])
         i32[1] = -1
     elsif deg == 270
         i32[0] = 0
         i32[1] = -1
     else
-        i32[0] = -(sin90[360 - deg])
+        i32[0] = ~(sin90[360 - deg])
         i32[1] = -1
     fin
     load32(@i32)
@@ -43,7 +44,7 @@ export def mulsin(val, deg)
     word[2] i32
     sin32(deg)
     muli16(val)
-    addi16($7FFF) // Round up
+    add32(@fprounding) // Round up
     store32(@i32)
     return i32[1]
 end
@@ -52,7 +53,7 @@ export def mulcos(val, deg)
     word[2] i32
     sin32(deg + 90)
     muli16(val)
-    addi16($7FFF) // Round up
+    add32(@fprounding) // Round up
     store32(@i32)
     return i32[1]
 end
diff --git a/src/mkrel b/src/mkrel
index fc8ca8f9..110189d2 100755
--- a/src/mkrel
+++ b/src/mkrel
@@ -182,6 +182,7 @@ cp scripts/bounce.4th prodos/bld/scripts/BOUNCE.4TH.TXT
 cp scripts/dbounce.4th prodos/bld/scripts/DBOUNCE.4TH.TXT
 cp scripts/hrbounce.4th prodos/bld/scripts/HRBOUNCE.4TH.TXT
 cp scripts/plot.4th prodos/bld/scripts/PLOT.4TH.TXT
+cp scripts/grturtle.4th prodos/bld/scripts/GRTURTLE.4TH.TXT
 cp scripts/hrplot.4th prodos/bld/scripts/HRPLOT.4TH.TXT
 cp scripts/hrturtle.4th prodos/bld/scripts/HRTURTLE.4TH.TXT
 cp scripts/gfxplot.4th prodos/bld/scripts/GFXPLOT.4TH.TXT
diff --git a/src/scripts/grturtle.4th b/src/scripts/grturtle.4th
new file mode 100644
index 00000000..fee952c9
--- /dev/null
+++ b/src/scripts/grturtle.4th
@@ -0,0 +1,29 @@
+SRC" PLASMA.4TH"
+SRC" CONIO.4TH"
+SRC" TURTLE.4TH"
+" LINES" LOADMOD"  "
+LOOKUP SETLINEPLOT PLASMA SETLINEPLOT
+PFA PLOT SETLINEPLOT
+
+: SHOW
+
+  GR
+  40 40 [ LOOKUP LINE ] LITERAL INITTURTLE
+;
+
+: SQUARE
+    DUP MOVEFORWARD 90 TURNRIGHT
+    DUP MOVEFORWARD 90 TURNRIGHT
+    DUP MOVEFORWARD 90 TURNRIGHT
+        MOVEFORWARD 90 TURNRIGHT
+;
+
+: SPIN
+    361 0 DO
+        I COLOR
+        15 SQUARE
+        I TURNTO
+    10 +LOOP
+;
+
+SHOW SPIN