diff --git a/lib/register/instruction.rb b/lib/register/instruction.rb
index 3e53acb2..13501cde 100644
--- a/lib/register/instruction.rb
+++ b/lib/register/instruction.rb
@@ -117,6 +117,7 @@ module Register
 
 end
 
+require_relative "instructions/setter"
 require_relative "instructions/set_slot"
 require_relative "instructions/get_slot"
 require_relative "instructions/set_byte"
diff --git a/lib/register/instructions/set_byte.rb b/lib/register/instructions/set_byte.rb
index 81641851..c2a3116c 100644
--- a/lib/register/instructions/set_byte.rb
+++ b/lib/register/instructions/set_byte.rb
@@ -4,22 +4,8 @@ module Register
 
   # indexes are 1 based !
 
-  class SetByte < Instruction
+  class SetByte < Setter
 
-    # If you had a c array (off int8) and index offset (>0)
-    # the instruction would do array[index] = register
-    # So SetByte means the register (first argument) moves to the slot (array and index)
-    def initialize source , register , array , index
-      super(source)
-      @register = register
-      @array = array
-      @index = index
-      raise "index 0 " if index == 0
-      raise "Not integer or reg #{index}" unless index.is_a?(Numeric) or RegisterValue.look_like_reg(index)
-      raise "Not register #{register}" unless RegisterValue.look_like_reg(register)
-      raise "Not register #{array}" unless RegisterValue.look_like_reg(array)
-    end
-    attr_accessor :register , :array , :index
     def to_s
       "SetByte: #{register} -> #{array} [#{index}]"
     end
diff --git a/lib/register/instructions/set_slot.rb b/lib/register/instructions/set_slot.rb
index 37a4ef7b..d0a3f1f0 100644
--- a/lib/register/instructions/set_slot.rb
+++ b/lib/register/instructions/set_slot.rb
@@ -4,30 +4,22 @@ module Register
   # GetSlot moves data into a register from memory.
   # Both use a base memory (a register)
 
-  # While the virtual machine has only one instruction (Set) to move data between slots,
-  # the register has two, namely GetSlot and SetSlot
-  #
   # This is because that is what cpu's can do. In programming terms this would be accessing
   #  an element in an array, in the case of SetSlot setting the register in the array.
 
   # btw: to move data between registers, use RegisterTransfer
 
-  class SetSlot < Instruction
+  class SetSlot < Setter
 
     # If you had a c array and index offset
     # the instruction would do array[index] = register
     # So SetSlot means the register (first argument) moves to the slot (array and index)
-    def initialize source , register , array , index
-      super(source)
-      @register = register
-      @array = array
-      @index = index
-      raise "index 0 " if index == 0
-      raise "Not integer or reg #{index}" unless index.is_a?(Numeric) or RegisterValue.look_like_reg(index)
-      raise "Not register #{register}" unless RegisterValue.look_like_reg(register)
-      raise "Not register #{array}" unless RegisterValue.look_like_reg(array)
-    end
-    attr_accessor :register , :array , :index
+
+    # def initialize source , register , array , index
+    # super
+    # end
+    # attr_accessor :register , :array , :index
+
     def to_s
       "SetSlot: #{register} -> #{array} [#{index}]"
     end
diff --git a/lib/register/instructions/setter.rb b/lib/register/instructions/setter.rb
new file mode 100644
index 00000000..1d72109f
--- /dev/null
+++ b/lib/register/instructions/setter.rb
@@ -0,0 +1,29 @@
+module Register
+  # Setter is a base class for set instructions (SetSlot and SetByte , possibly more coming)
+  #
+  # The instruction that is modelled is loading data from an array into a register
+  #
+  # Setter has a
+  # - Register that the data is moved to
+  # - an array where the data comes from
+  # - and (array) index
+  class Setter < Instruction
+
+    # If you had a c array and index offset
+    # the instruction would do array[index] = register
+    # So Setter means the register (first argument) moves to the slot (array and index)
+    def initialize source , register , array , index
+      super(source)
+      @register = register
+      @array = array
+      @index = index
+      raise "index 0 " if index == 0
+      raise "Not integer or reg #{index}" unless index.is_a?(Numeric) or RegisterValue.look_like_reg(index)
+      raise "Not register #{register}" unless RegisterValue.look_like_reg(register)
+      raise "Not register #{array}" unless RegisterValue.look_like_reg(array)
+    end
+    attr_accessor :register , :array , :index
+
+  end
+
+end