From the ET-73 Manual:
The Redi Chek® Remote registers temperatures as low as 14 °F (-10 °C) and as high 410 °F (210 °C). LLL will
be displayed below 14 °F and HHH will be displayed above 410 °F. Do not use the stainless steel probe sensor
above 410 °F. Doing so will deteriorate the wire.
JimT