To set the xrange to the default:
set xrange [-10:10]
To set the yrange to increase downwards:
set yrange [10:-10]
To change zmax to 10 without affecting zmin (which may still be autoscaled):
set zrange [:10]
To autoscale xmin while leaving xmax unchanged:
set xrange [*:]
To autoscale xmin but keeping xmin positive:
set xrange [0<*:]
To autoscale x but keep minimum range of 10 to 50 (actual might be larger):
set xrange [*<10:50<*]
Autoscaling but limit maximum xrange to -1000 to 1000, i.e. autoscaling within [-1000:1000]
set xrange [-1000<*:*<1000]
Make sure xmin is somewhere between -200 and 100:
set xrange [-200<*<100:]