anchor.diff:  
   calc_update(NewState, Entity, []) ->
   	OldState = Entity#entity.state,
  +	NewEntity = Entity#entity{
  +		state = NewState
  +	},
   	case diff_state(OldState, NewState) of
   		[] ->
  -			{undefined, Entity};
  +			{undefined, NewEntity};
   		Update ->
  -			NewEntity = Entity#entity{
  -				state = NewState
  -			},
   			{Update, NewEntity}
   	end;
   
  
positive.code: 	[{Key :: binary(), Value::term()}].
  
  diff_state(OldState, NewState) ->
  	dict:fold(fun(Key, NewValue, AccIn) ->
  		OldValue = dict:fetch(Key, OldState),
  		case NewValue == OldValue of
  			false ->
  				case Key of
  					physical ->
  						[{Key, pre_physics_rk4:diff_to_proplist(OldValue, NewValue)} | AccIn];
  						%[{Key, pre_physics_rk4:to_proplist(NewValue)} | AccIn];
  					_ ->
  						[{Key, NewValue} | AccIn]
  				end;
  			_ ->
  				AccIn
  		end
  
negative.code: 
  %% --------------------------------------------------------------------------------------------------------------------
  
  %% @doc Returns the difference of two state dictionaries.
  %%
  %% Assumes that both states are dictionaries, returns a list of tuples of Key, Value.
  