Your thermometer.php is at V1.13 and current is V1.15, but that shouldn't change the WD display (both work with PHP 7+).
The autoscale is engaged only when the max is above the $TmaxF setting, or the min is below the $TminF setting -- then the scale is adjusted by $TincrF degrees (up for max, down for min) but a new min won't change the max displayed value and vice versa -- the scale doesn't shrink, it only expands.