Negative spread quote? Impossible?

[13th]

Hi,

I need help understanding some price quote for combos.

When I chart a vertical spread on TWS, a lot of times I'm seeing negative price history for for buying spreads. It's hard to put it into words for me. Just take a look at the chart.

Technically, this should be impossible. Higher strike puts should always be more expensive then lower strike puts, right?

 

[nazzdack]

----understanding some price quote for combos.
----vertical spread....
----negative price history....
----hard to put it into words....
----Higher strike puts should always be more expensive then lower strike puts....
----right?

1) ? ...... I would guess that the "negative quote" is merely the "negative" of the outright premium on the 1875-put strike-price.
2) Somehow, someway, a calculation of "Zero minus the 1875 put-premium" is being calculated and charted. The result will be a negative number. :eek:

 

[13th]

1) ? ...... I would guess that the "negative quote" is merely the "negative" of the outright premium on the 1875-put strike-price.
2) Somehow, someway, a calculation of "Zero minus the 1875 put-premium" is being calculated and charted. The result will be a negative number. :eek:

Oh, ok. This sheds some light on this situation. Its only 1850 put is being charted, because i think that 1875 put quotes were not available. No one was trading them, so the machines only assume 1875 put value at zero, and plot only 1850 put value, which if sold would yield only a credit, i.e. 1850 put - 0

Thx a lot nazzdack!