diff --git a/model/types.go b/model/types.go
new file mode 100644
index 0000000..9d3ed05
--- /dev/null
+++ b/model/types.go
@@ -0,0 +1,43 @@
+package model
+
+import "time"
+
+// Note holds a text note along with the time the note was taken.
+type Note struct {
+	Time time.Time `json:"time"`
+	Text string    `json:"text"`
+}
+
+// NewNote returns a new Note
+func NewNote(text string) Note {
+	return Note{
+		Time: time.Now(),
+		Text: text,
+	}
+}
+
+// Reading holds the glucose and ketone level measurements along with the time the measurements were taken.
+type Reading struct {
+	Time    time.Time `json:"time"`
+	Glucose float64   `json:"glucose"`
+	Ketone  float64   `json:"ketone"`
+	GKI     float64   `json:"GKI"`
+}
+
+// NewReading creates and returns a new Reading instance with the provided glucose and ketone levels, and records
+// the current time. The glucose value should be provided in mg/dL, while the ketone level should be in mmol/L.
+func NewReading(glucose, ketone float64) Reading {
+	var gki float64
+	if ketone == 0 {
+		gki = 0
+	} else {
+		gki = (glucose / 18) / ketone
+	}
+
+	return Reading{
+		Time:    time.Now(),
+		Glucose: glucose,
+		Ketone:  ketone,
+		GKI:     gki,
+	}
+}