Sometimes, even at Bletchley Park, everyday problems like drafty buildings must have intruded on the work of Alan Turing and the other brilliant minds cracking the Germans’ "Enigma" code. At least, enough so that notes used to break the code were wadded up and stuffed into cracks to better insulate Hut 6.

During the building’s restoration in 2013, part of a huge effort to restore the historic complex, the notes and other documents were found and immediately preserved, NBC News reports. Now they’ve been restored in time for a soon-to-open exhibition. Like Turing’s notebook, soon up for auction, the documents give us a peek into that time.

“The fact that these papers were used to block drafty holes in the primitive hut walls reminds us of the rudimentary conditions under which these extraordinary people were working,” Iain Stander, chief executive of the Bletchley Park Trust, told Jessica Duncan for MKWeb. Duncan reports that several other artifacts were discovered during the restoration, including a piece of a 1940s teapot, glass bottles and a time capsule left inside Hut11A’s door.

Some of the papers are Banbury sheets, named for a code-breaking technique called Banburismus. The website I Programmer explains how they were used:

Banburismus was a cryptanalysis procedure that took advantage of operator shortcomings in the Enigma encoding that could reveal the position of the rotor by noticing overlaps of letters in two messages. Banbury sheets were used to look for overlaps. Two cipher tests were punched onto different sheets and the sheets were slid past one another.

Finding new documents from that time is rare, notes the BBC, because many were destroyed after WWII to keep the methods secret. The rest are already stored in the Park’s archives. Some of the other papers are handwritten.

“These are the actual documents used by codebreakers, and in terms of the codebreaking process they are pivotal,” Gillian Mason, Bletchley Park curator, told MKWeb. “I can just see these people beavering away. There is a lot of pencil and crayon activity.”