diff --git a/src/interval.cpp b/src/interval.cpp
index e955999..3125c92 100644
--- a/src/interval.cpp
+++ b/src/interval.cpp
@@ -1,19 +1,19 @@
 #include "interval.h"
 
 // Public Methods //////////////////////////////////////////////////////////////
-uint32_t Interval::remains(void)
+uint32_t Interval::remains() const
 {
 
     return _timeout - (millis() - _timefrom);
 }
 
-uint32_t Interval::elapsed(void)
+uint32_t Interval::elapsed() const
 {
 
     return millis() - _timefrom;
 }
 
-bool Interval::expired(void)
+bool Interval::expired()
 {
     bool result = false;
 
@@ -66,7 +66,7 @@ void Interval::setPeriodic(uint32_t tmout)
     _done = 0xff;
 }
 
-void Interval::reload(void)
+void Interval::reload()
 {
 
     _timefrom = millis();
diff --git a/src/interval.h b/src/interval.h
index cd4e0de..4507f41 100644
--- a/src/interval.h
+++ b/src/interval.h
@@ -1,8 +1,7 @@
-#ifndef _INTERVAL_H_
-#define _INTERVAL_H_
+#pragma once
 
 /* Interval
- * Copyright (C) 2014, 2016, 2018, 2019  Pavel Brychta http://www.xpablo.cz
+ * Copyright (C) 2014, 2016, 2018, 2019, 2023  Pavel Brychta http://www.xpablo.cz
  *
  * This program is free software: you can redistribute it and/or modify it under the terms of the MIT License
  */
@@ -12,21 +11,21 @@
 class Interval
 {
 protected:
-    uint32_t _timefrom;
-    uint32_t _timeout;
-    uint8_t _mode; // mode of actual operation (compatibility, oneshot, periodic)
-    uint8_t _done;
+    uint32_t _timefrom = 0;
+    uint32_t _timeout = 0;
+    uint8_t _mode = 0; // mode of actual operation (compatibility, oneshot, periodic)
+    uint8_t _done = 0xff; // compatibility mode autostart
 public:
-    Interval():_timefrom(0), _timeout(0), _mode(0), _done(0xff) {} // compatibility mode autostart
-    Interval(uint32_t tmout): _timefrom(0), _timeout(tmout), _mode(2), _done(0xff) {} // periodic mode autostart
-    bool expired(void);
+    Interval() = default;
+    explicit Interval(uint32_t tmout)
+        : _timeout(tmout)
+        , _mode(2) // periodic mode autostart
+    {}
+    bool expired();
     void set(uint32_t tmout);
     void setOneshot(uint32_t tmout);
     void setPeriodic(uint32_t tmout);
-    void reload(void);
-    uint32_t elapsed(void);
-    uint32_t remains(void);
+    void reload();
+    [[nodiscard]] uint32_t elapsed() const;
+    [[nodiscard]] uint32_t remains() const;
 };
-
-#endif
-// EOF