diff --git a/Machines/CRTMachine.hpp b/Machines/CRTMachine.hpp
index 9cc2f869f..0a192a3c7 100644
--- a/Machines/CRTMachine.hpp
+++ b/Machines/CRTMachine.hpp
@@ -23,12 +23,25 @@ class Machine {
 	public:
 		Machine() : clock_is_unlimited_(false) {}
 
+		/*!
+			Causes the machine to set up its CRT and, if it has one, speaker. The caller guarantees
+			that an OpenGL context is bound.
+		*/
 		virtual void setup_output(float aspect_ratio) = 0;
+
+		/*!
+			Gives the machine a chance to release all owned resources. The caller guarantees that the
+			OpenGL context is bound.
+		*/
 		virtual void close_output() = 0;
 
+		/// @returns The CRT this machine is drawing to. Should not be @c nullptr.
 		virtual std::shared_ptr<Outputs::CRT::CRT> get_crt() = 0;
+
+		/// @returns The speaker that receives this machine's output, or @c nullptr if this machine is mute.
 		virtual std::shared_ptr<Outputs::Speaker> get_speaker() = 0;
 
+		/// Runs the machine for @c number_of_cycle cycles.
 		virtual void run_for_cycles(int number_of_cycles) = 0;
 
 		// TODO: sever the clock-rate stuff.