diff --git a/compiler/global/clocks.ml b/compiler/global/clocks.ml
index 0558f7b..8bb2f4b 100644
--- a/compiler/global/clocks.ml
+++ b/compiler/global/clocks.ml
@@ -104,6 +104,10 @@ let prod ck_l = match ck_l with
   | [ck] -> Ck ck
   | _ -> Cprod (List.map (fun ck -> Ck ck) ck_l)
 
+let rec root_ck_of ck = match ck_repr ck with
+  | Cbase | Cvar _ -> ck
+  | Con(ck,_,_) -> root_ck_of ck
+
 (*
 let rec tuple ck = function
   | Tprod ty_list ->
diff --git a/compiler/global/global_printer.ml b/compiler/global/global_printer.ml
index a102d24..4d4a422 100644
--- a/compiler/global/global_printer.ml
+++ b/compiler/global/global_printer.ml
@@ -146,7 +146,7 @@ let print_ident ff id = Format.fprintf ff "%s" (name id)
   | Cbase -> fprintf ff "base"
   | Con (ck, c, n) ->
       fprintf ff "%a on %a(%a)" print_ck ck print_qualname c print_ident n
-  | Cvar { contents = Cindex _ } -> fprintf ff "base"
+  | Cvar { contents = Cindex i } -> fprintf ff "'a%i" i
   | Cvar { contents = Clink ck } -> print_ck ff ck
 
 let rec print_ct ff = function
diff --git a/compiler/minils/analysis/clocking.ml b/compiler/minils/analysis/clocking.ml
index a3eac0e..74cd89e 100644
--- a/compiler/minils/analysis/clocking.ml
+++ b/compiler/minils/analysis/clocking.ml
@@ -139,7 +139,7 @@ let typing_eq h { eq_lhs = pat; eq_rhs = e } =
           | Some(reset) -> ck_of_name h reset in
         let ct = typing_app h ck_r pat op args in
         ct, ck_r
-    | Eiterator (_, _, _, pargs, args, r) ->
+    | Eiterator (_, _, _, pargs, args, r) ->        (*TODO*)
         (* Typed exactly as a fun or a node... *)
         let ck_r = match r with
           | None -> fresh_clock()
@@ -147,7 +147,6 @@ let typing_eq h { eq_lhs = pat; eq_rhs = e } =
         in
         List.iter (expect_extvalue h ck_r) pargs;
         List.iter (expect_extvalue h ck_r) args;
-        (*TODO*)
         Ck ck_r, ck_r
   in
   e.e_base_ck <- base;
@@ -191,11 +190,13 @@ let typing_contract h contract =
         append_env h c_list
 
 let typing_node node =
-  let h = append_env Env.empty node.n_input in
-  let h = append_env h node.n_output in
-  let h = typing_contract h node.n_contract in
+  let h0 = append_env Env.empty node.n_input in
+  let h0 = append_env h0 node.n_output in
+  let h = typing_contract h0 node.n_contract in
   let h = append_env h node.n_local in
   typing_eqs h node.n_equs;
+  (* synchronize input and output on base : find the free vars and set them to base *)
+  Env.iter (fun id ck -> unify_ck (root_ck_of ck) Cbase) h0;
   (*update clock info in variables descriptions *)
   let set_clock vd = { vd with v_clock = ck_repr (Env.find vd.v_ident h) } in
   let node = { node with n_input = List.map set_clock node.n_input;
diff --git a/compiler/minils/analysis/level_clock.ml b/compiler/minils/analysis/level_clock.ml
new file mode 100644
index 0000000..63fc0a5
--- /dev/null
+++ b/compiler/minils/analysis/level_clock.ml
@@ -0,0 +1,32 @@
+(**************************************************************************)
+(*                                                                        *)
+(*  Heptagon                                                              *)
+(*                                                                        *)
+(*  Author : Marc Pouzet                                                  *)
+(*  Organization : Demons, LRI, University of Paris-Sud, Orsay            *)
+(*                                                                        *)
+(**************************************************************************)
+
+open Clocks
+open Minils
+
+(* Any clock variable left after clocking is free and should be set to level_ck.
+   Since inputs and outputs are grounded to Cbase, this append when
+   no data dependance exists between an expression and the inputs/outputs.*)
+
+(* We are confident that it is sufficient to unify level_ck with base_ck
+   for expressions having a base_ck == Cvar.
+   The other ones are coming from one like this one,
+   indeed if it was Con (Cvar,c,x) x would have to be defined with an expression of clock Cvar.*)
+
+let exp _ acc e =
+  let _ = match ck_repr e.e_base_ck with
+    | Cvar ({contents = Cindex _}) -> unify_ck e.e_base_ck e.e_level_ck
+    | _ -> ()
+  in
+  e,acc (* no recursion since in minils exps are not recursive *)
+
+let program p =
+  let funs = { Mls_mapfold.defaults with Mls_mapfold.exp = exp } in
+  let p, _ = Mls_mapfold.program_it funs [] p in
+  p
\ No newline at end of file
diff --git a/compiler/minils/main/mls_compiler.ml b/compiler/minils/main/mls_compiler.ml
index 8a42098..e30b984 100644
--- a/compiler/minils/main/mls_compiler.ml
+++ b/compiler/minils/main/mls_compiler.ml
@@ -17,6 +17,9 @@ let compile_program p =
   (* Clocking *)
   let p = pass "Clocking" true Clocking.program p pp in
 
+  (* Level clocks *)
+  let p = pass "Level clock" true Level_clock.program p pp in
+
   (* Check that the dataflow code is well initialized *)
   (*let p = silent_pass "Initialization check" !init Init.program p in *)
 
diff --git a/compiler/minils/mls_printer.ml b/compiler/minils/mls_printer.ml
index aaa28e8..10b00f3 100644
--- a/compiler/minils/mls_printer.ml
+++ b/compiler/minils/mls_printer.ml
@@ -27,19 +27,7 @@ let rec print_pat ff = function
   | Evarpat n -> print_ident ff n
   | Etuplepat pat_list ->
       fprintf ff "@[<2>(%a)@]" (print_list_r print_pat """,""") pat_list
-(*
-let rec print_ck ff = function
-  | Cbase -> fprintf ff "base"
-  | Con (ck, c, n) ->
-      fprintf ff "%a on %a(%a)" print_ck ck print_qualname c print_ident n
-  | Cvar { contents = Cindex _ } -> fprintf ff "base"
-  | Cvar { contents = Clink ck } -> print_ck ff ck
 
-let rec print_ct ff = function
-  | Ck ck -> print_ck ff ck
-  | Cprod ct_list ->
-      fprintf ff "@[<2>(%a)@]" (print_list_r print_clock """ *""") ct_list
-*)
 let print_vd ff { v_ident = n; v_type = ty; v_clock = ck } =
   if !Compiler_options.full_type_info then
     fprintf ff "%a : %a :: %a" print_ident n print_type ty print_ck ck
diff --git a/test/good/current.ept b/test/good/current.ept
index 77b71a9..7a31172 100644
--- a/test/good/current.ept
+++ b/test/good/current.ept
@@ -11,9 +11,11 @@ let
   y = x_cur when c
 tel
 
-node use_current (c : bool; x : int) returns (y : int on c)
-var x_cur :int;
+node use_current (c : bool; x : int) returns (b : bool on c; y : int on c)
+var x_cur, y2 :int;
 let
   x_cur = current(c,x);
   y = x_cur when c;
+  y2 = internal_current(c,x);
+  b = y = y2;
 tel
diff --git a/test/good/side_effet.ept b/test/good/side_effet.ept
new file mode 100644
index 0000000..f0eb3a9
--- /dev/null
+++ b/test/good/side_effet.ept
@@ -0,0 +1,10 @@
+node hello() returns (b:bool)
+var tmp : bool;
+let
+  tmp = (*printf("hello")*) true;
+  automaton
+  state A var ttmp :bool; do
+    b = true;
+    ttmp = (*printf("hello")*) true;
+  end;
+tel