Sheet Grid Position Marker Dots

Hi.
Can anyone explain to me what the grids are in the margins on UK stamp sheets? I have a British DataMatrix £3.50 stamp with the margin attached. There is a small 2x8 grid with a dot in one of the boxes and I am curious to know what this is. I have come across the term "sheet grid position marker dots", but with no further details. What is a sheet grtid?
The stamp is from a Counter Sheet of 25 stamps. When I scan the datamatrix, it shows up as being position 51 on the sheet (?!)
Photo attached.

Thanks

It says that your stamp was part of the counter sheet that was the fourth sheet in the first row of the printer's sheet.
These sheets were printed eight at the time.

You should turn it on its side. Counter sheets were printed sideways.

I believe it shows the position of your sheetlet on the actual complete sheet when it came off the press


Peter

interesting, being top left, i,e, in the first position, the possibilities are 01, 26, 51, or 76. You would expect 51 to be from the top left of the third sheet from a row, Then again,that assumes the first sheet in the batch started with iten number ??????01. Who is to say it did not start with ??????26.

For those unfamiliar with the data matrix coding on UK permanent and Christmas stamp, the data matrix will have the following format:

JGBS19901017031000237380025519012201 A4941979CE74410A01

The latter part is a control, the first contains data on the stamp:

JGB is the UPU code for the United Kingdom.

S1?? is a tariff code, S199 is for stamps with a face value.

The next number identifies the source. 0 is a strip of stamps to be used on an FDC. OP's stamp will have had the number 4.

The following seven numbers (1017031) are the same for all stamps and are the supply chain ID.

The following eight positions are an item number; here it is 00023738. OP's "position 51'" would have this number end in "51."

Then comes the value in pence (here 00255, or £ 2.55). OP's stamp will have had 00350.

The following six numbers are a date: 19-01-2022. It is not the production date but tends to be within one ortwo months of it. It may have to do with the serring up of the data matrix printing unit.

The final two positions identify the type of stamp: "01" is a national permanent (definitive) stamp.