Need Some Help With Machin's Block Of 4

Somehow I wound up with a pile of Machins. So, I figured I would try to organize them a little. Digging around I found this.


I can identify the Machin's but not the configuration or block.

Thanks.

They'll be part of a booklet pane surely?

Stanley Gibbons # X845L ?
Caveat: I am unable to read the "source"
Machin specialists welcome to educate me.

PS: with Machins, it is always beneficial to list phosphor type, if any.

I agree, this looks like SG X845l.

I believe it comes one of the two "London 1990" 10p folded booklets, SG FA10 or FA11.

I was guessing a London 1980 booklet. The 8 is higher than the 1 on the adjacent stamp, so first printing from 1979? I am no Machin expert.

Got it.
SG#845L Booklet Pane. Number X879 and X845 x 2 plus label 17th October 1979
Always learning

So, note to self,
1. Locate Booklet Pane Guide and note number
2. Source stamp ID by Colour, face value and phosphor
3. Look up index of lowest value to determine "source"

Example Booklet pane Guide

You guys are just AWESOME!

Thank you, always learning!

Next question. Is there a Gibbons speciality catalog for Machin's? I've got the 2019 Stanley Gibbons and can't find a listing specific to the #845L booklet pane.

SG 845l is listed in the SG Great Britain Concise catalogue.

Thank you. Just ordered the Great Britain Concise catalog.

@Moyock13

The Stanley Gibbons Great Britain Specialised Stamp Catalogue Queen Elizabeth II Decimal Definitive Issues: vol. 4, is one with a specialised Machin listing that also includes booklets and booklet panes. The Concise also lists booklets and panes.

The label at the top left identifies it as coming from a booklet.

Don't forget the obvious the cancellation says 21st January 1983. So it isn't from a later date.
I don't collect Machins in greater depth than the SG concise catalogue, to help me identify the colour of stamps I have started to acquire Machin first day covers and booklet panes which due to there combination of stamps and date can be identified more definitely, these act as a reference for identifying colour.