Queen Elizabeth II, 1 1/2 Pence With Black Lines On Backside

I have this 1 queen stamp out of so many similar QE II's stamps but with 2 vertical lines at the back. is it some thing rare? the watermarks appears to be St Edwards.
thanks

Graphite lines, for registering. Worth checking whether there are two phosphor bands on the front, as there is an uncommon variety from 1959 which has graphite lines but no phosphor bands.

They were used for automated mail processing.

Jack Kelley

So it should be noted that the 1-1/2p green is the most uncommon of the 8 denominations that had graphite lines. In my 2006 catalog it has a value of $92.50 which is a tad more than the $.20 for those that lack the lines

Here's a copy of my version. Although it is difficult to see, watermark inverted is normal for this issue. However, SG notes that the value of watermark upright is the same.

I got a bit confused
As per SG the CV is 92 dollars? Anyone can share the SG number n details.

watermark St Edward's Crown SG563 - specialised S27 - CV £ 0.30 only upright, 1998 specialised vol. 3
watermark Crowns SG 589 - specialised S30 - CV £ 95 wmk upright or £ 40 wmk inverted. Inverted is more common, but these are from booklets and those tend to havee 50% panes with upright and 50% with inverted wmk.
Of course, the CV is for examples with good perforations. The value drops significantly with perforatins cut close.
watermark St. Edward's Crown with green-reacting phosphor on front SG 601 - specialised S31 - CV £ 2.00, only upright

thanks to everyone, I was under an impression that this one would be of higher value due to the graphite line.

If it is the ordinarry St. Edward's Crown one, the fact that it is cancelled makes it have a £ 2 CV instead of £ 0.30 unmounted mint.

The graphite lines were used as in an experiment in automatic sorting of mail. The experiments were based around Southampton. The ink went under the trade name Napthadag the DAG being an acronym for the active content of the ink used to print the lines: which was deflocculated Atchesons graphite.