Autoclave and autoclave tape

The autoclave is like a huge pressure cooker that heats under high pressure with steam to sterilize labware, liquid & lab wastes. It must reach & maintain at 121°C for at least 15 min to be effective. This process can inactivate bacterial spores, viruses & fungi. ⠀
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The autoclave tapes are used & taped on the external of the item during autoclave. However, this only indicates that the temperature is reached & not an indicator of whether the items are sterilized. Do you know the other indicators for autoclave sterilization?