diff --git a/web/image_conveyor_reference_autosave_math.mjs b/web/image_conveyor_reference_autosave_math.mjs
new file mode 100644
index 0000000..df80820
--- /dev/null
+++ b/web/image_conveyor_reference_autosave_math.mjs
@@ -0,0 +1,25 @@
+import { normalizeReferenceSlots } from './image_conveyor_math.mjs'
+
+export function referencePresetStateSnapshot(state) {
+  const source = state && typeof state === 'object' ? state : {}
+  const presetId = String(source.active_reference_preset_id ?? '').trim()
+  const slots = normalizeReferenceSlots(source.reference_slots)
+  return {
+    presetId,
+    slots,
+    slotKey: JSON.stringify(slots.map((slot) => slot?.annotated || ''))
+  }
+}
+
+export function shouldAutosaveReferencePreset(previous, current) {
+  if (!previous || !current?.presetId) return false
+  if (previous.presetId !== current.presetId) return false
+  return previous.slotKey !== current.slotKey
+}
+
+export function referencePresetSaveKey(presetId, slots) {
+  const normalizedId = String(presetId ?? '').trim()
+  if (!normalizedId) return ''
+  const normalizedSlots = normalizeReferenceSlots(slots)
+  return `${normalizedId}:${JSON.stringify(normalizedSlots.map((slot) => slot?.annotated || ''))}`
+}