diff --git a/dmx/universe.cpp b/dmx/universe.cpp
index 0d05888..e4d4684 100644
--- a/dmx/universe.cpp
+++ b/dmx/universe.cpp
@@ -25,7 +25,6 @@
 #include "universe.h"
 
 namespace DMX {
-using std::copy;
 
 /**
 */
@@ -33,6 +32,19 @@ Universe::Universe() {
   null_start_data_.fill(0);
 }
 
+/**
+   Get value of a slot.
+
+   @param uint16_t address of the requested slot.
+   @return const uint8_t value of the slot.
+*/
+const uint8_t Universe::slot (uint16_t address) const
+{
+    if (address > 512) return 0;
+    return null_start_data_[address];
+}
+
+
 /**
    accept new data from receiver
 
@@ -42,7 +54,7 @@ void Universe::set(vector<uint8_t> vect) {
   switch (vect.front()) { // start code
     case E111_NULL_START:
       vect.resize(null_start_data_.size(), 0); // pad shorter, truncate larger
-      copy(vect.begin(), vect.end(), null_start_data_.begin());
+      std::copy(vect.begin(), vect.end(), null_start_data_.begin());
       for (const auto &cb : callbacks_)
         cb(this);
       break;
diff --git a/dmx/universe.h b/dmx/universe.h
index fccad62..1b89777 100644
--- a/dmx/universe.h
+++ b/dmx/universe.h
@@ -59,10 +59,11 @@ class Universe {
   public:
     Universe ();
 
-    DimmerData * data() { return &null_start_data_; }
-    void    onData (const DataHandler callback);
-    void    set    (vector<uint8_t>);
-    uint8_t slot   (uint16_t address) { return null_start_data_[address]; }
+    const DimmerData * data() const { return &null_start_data_; }
+    const uint8_t slot (uint16_t address) const;
+
+    void set (vector<uint8_t>);
+    void onData (const DataHandler);
 
   private:
     DimmerData null_start_data_;