(I also don't know what they mean
by '1200 amps R Resistive or 1200 amps Tungsten', but you are nut if you
think you're going to put 1200A into anything safe.}

Mike meant to type "Watts" rather than "Amps".

The "Resistive" rating refers to a constant resistive load. The
"Tungsten" rating refers to a (tungsten filament) incandescent lamp load.

Tungsten has a positive temperature coefficient of resistance, so a cold
lamp filament has a much lower resistance than it does at operating
temperature. The reason one sometimes sees a lower "Tungsten" rating
specified for switches and relays is because when an incandescent lamp
is turned on it results in a high initial surge current until the
filament heats up.

John