2-2c Red Booklets On First Flight Registered

It is unopened, any ideas which booklets these could be?
Is this worth hanging onto?

Yes it is a cover worth holding on to due to the booklet pane usages both of which are positional piece booklet panes. Per the postmarks, this traveled from San Francisco, CA to Sharon, PA with no indication Chicago was included as a stop. The cachet indicates the 7-1-1927 Chicago to San Francisco trip, this being in the other direction leaving on the same day. Someone with the airmail catalog handy perhaps will chime in as to if the flights were undertaken in both direction on the same date. I don't have my Scoot handy for determining the particular booklet panes at the moment.

Edit: 406a if perf. 12; 499e if perf. 11; if perf.10, 425e or 463a depending on watermark.

Being a registered envelope, it would have been enclosed in a "registered paper jacket envelope", which would have received the various transit markings. The backstamps of only the orign and destination post offices are quite normal for registered mail. With the origin and destination marks on consecutive days, there is not doubt it flew by some route.

Thought this was interesting to add some color to the topic:






https://mohai.org/collections-and-r...ry&pageNum=2

parcel post wrote: "both of which are positional piece booklet panes". you said that because you see center lines on each booklet? One vertical and one horizontal.

yes (right & bottom)

both panes are perf. 10s so either 425e or 463a

The cover contains a surprisingly late use of either 425e (issued in 1914) or 463a (issued in 1916). 1927 is several years after 554c was issued in huge quantities so that booklet pane would be "normal" on a 1927 cover. Roughly 3.5 times more 425e were printed than 463a so the chance is your cover contains "leftover" 425e panes.

In any case, the pane with a right and bottom guide line is scarce on or off cover (only max. 1.6% of all panes can show this mark).
In combination with a first flight cachet, this is a highly collectible cover.

The left booklet pane has a center line at the right and at the bottom. The right pane has the center line only on the bottom. Depending on the registration of the panes as cut the vertical center line will show on the right, left or both panes separated by that center line. For the horizontal center line, it will show at the bottom, top or both depending on the registration of the panes when cut.

Only four pane positions can show the crossing center lines (bottom or top and left or right). For the horizontal line (top or bottom) only 12 panes can have just this line. Due to the arrows ending each line, if some of it is captured when the panes are cut, then there are four position possible as edge plate panes; however, if the arrow is not captured, the pane will look like one of the horizontal center line only positions.

For the vertical line, there are only four panes which will show that alone. The top most and bottom most panes, if cut to capture part of the arrow, will be a different, plate edge, position; however if not capturing the arrow, then they will look like the one of the vertical line only positions.

There are 60 total panes produced from such a plate layout.

See: https://www.stampcommunity.org/topi...PIC_ID=12766 for a discussion on the 360 Subject Booklet Plate Layout with illustrations

Not shown in the OP cover are the two most difficult positions to find the top with a plate number which will always show in the top tab of the pane as normal production. Requiring some level of registration of pane cutting, the other single plate positions are the pane with the bottom plate number and any of the four corners.

Thank you for the informative information!! :)