diff --git a/include/reading.hpp b/include/reading.hpp
new file mode 100644
index 0000000..857cffa
--- /dev/null
+++ b/include/reading.hpp
@@ -0,0 +1,8 @@
+#pragma once
+#include <cstdint>
+#include <string>
+
+struct Reading { std::string channel; double celsius; std::int64_t timestamp_ms; };
+enum class ChannelState { Healthy, Stale, OutOfRange };
+struct ChannelAssessment { Reading reading; ChannelState state; };
+ChannelAssessment assess_channel(const Reading& reading, std::int64_t now_ms);