Steve, thanks for that info on the reset button , I go through this every time I change batteries. I put a note on the back of my Springfield temp now.
Two possibilities, one with boiling hot water the other with some ice cubes in a cup.
immerse the thermometer in a jar of boiling water and adjust the themeometer to read 100C or 212F hold it down witha piece of adehasive tape firmly and glue it.
Or imerse it a jar of ice with water so that the ice begins to melt and adjust the themometer murcury line to line up with 0C or 32F firmly with tape and glue it in place.
You are done