New Zealand Sg931 - A Question, Please.

Here's a block of four SG931 from a series which I find visually very appealing. This is a lower left corner block, presumably from the left pane as the left bar of the registration crosses can be seen in the right margin and these normally reside in the inter-pane gutter. The margin also displays the traffic lights.

My question is: What is the "Side Lay" referred to in the margin?

First time for me to read this phrase.
"Askphil"...nothing there.

Side lay often referred to in NZ auction pages.

From Google:

In a letter of 17 September 1990 to the exhibitor, Harrisons explained that the error was caused by the sheet not having gone up to the side lay or grip edge of the printing machine in the right position, resulting in the design being printed in the wrong position. The stamps were perforated correctly.

Thanks, Rod. I suspected that was the answer but thought that, in the printing context, "sidelay" was a single word.

If that is the meaning in this case, it seems odd to print it on the sheet as if this will cause the sheets to line up magically before printing or perforating (;-)