There is a peculiar smell that comes from old paper. It’s a mix of lignin breakdown, dust, and the faint ghost of cigarette smoke from the 1980s. If you are holding a physical copy of the Sigma 161 manual , you know that smell well. If you are searching for a PDF of it at 2:00 AM, you are likely frustrated—but also curious.

If you are looking for the manual for a Sigma 161 industrial thermostat : Call an electrician. That manual is written in engineering shorthand that predates modern wiring codes. If you have a physical copy of the Sigma 161 manual sitting in your attic, please, scan it . Upload it to Archive.org. Post it on a subreddit. There is someone in the world right now staring at a blinking red light on a box of metal, holding a hotshoe adapter, wondering why the test button doesn't work.

You hold the key to their frustration. Do you own a Sigma 161? Are you looking for the flash or the industrial unit? Let me know in the comments—I might have a scanned PDF to share.