Hi @JUSTBOB, when I co-founded HC back in early 1990s, it was...

Hi @JUSTBOB,  when I co-founded HC back in early 1990s, it was $25 per SPI point.  I just checked one discussion log I have.  Here is some excerpts below:

lets say this morning you think allors/spi is still quite weak and
   therefore view the open (which because of dow, will be higher than
   yesterdays close) as a sell
you would sell the spi (let's say at 2716) on the open at 9:50am
now you are short spi
and you want it to fall in price, to buy back later on at a lower level,
   and thus lock in a profit
now the spi doesnt care how long you hold it
it's got a september expiry but most likely you will be out b4 then
(many people wil be out b4 the end of the day)
let's say you were right
and spi falls
and this afternoon it is trading at 2690
you decide to buy the position back at that price and thus lock in a 26
   point profit
26 x $25 = $650
of course, you could hold for longer
let's say you bought it back next week at 2650
now thats a bigger profit
66 x $25 = $1650

66 x $25 = $1650
if spi went up instead you would cut a loss perhaps at say 2730
> so u can buy for any number like 2516, 2713, 2817, etc
you can buy or sell where it is trading
market is constantly trading, just like a stock