Uploaded November 2024 | Updated September 2026, 2 weeks ago

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A generous Patron donated this incredible analog-electro-opto-mechanical clock that was once used to synchronize the world to a microsecond. Let's find out what makes it tick, literally.

HP 115BR Playlist: youtube.com/playlist?list=PL-_93BVApb5-_7sWRxQ0on8vNy7_H-zxS
Atomic clock playlist: youtube.com/playlist?list=PL-_93BVApb59F6V90OdcqVofqVWceR6Dk

Link to the HP 115BR Manual: bama.edebris.com/download/hp/115br/HP_115BR_frequency_divider_and_clock_op_service_manual_1967.pdf

Stuff that supports the channel:
- Support us on Patreon: patreon.com/curiousmarc
- Amazon links for the tools I use in the lab: curiousmarc.com/amazon-links
- Channel merch on Fourthwall: curiousmarc-shop.fourthwall.com
- Legacy channel merch on Teespring (I don't have everything transferred to Fourthwall yet): teespring.com/stores/curiousmarcs-store

"Elevator Music" Credit: Crinoline Dreams by Kevin MacLeod

Our lovely sponsors
- PCBWay: fast turn PCBs, pcbway.com
- Electro-Rent: electrorent.com
- Keysight: test instruments: keysight.com
- Samtec: connectors: samtec.com
- R&D Microwaves: rdmicrowaves.com

Get more technical info on the companion site: curiousmarc.com
Contact info: youtube.com/curiousmarc/about

00:00 Intro to the HP 115BR clock
01:55 The very special synchronization feature
03:05 The 1964 flying atomic clock experiment
04:10 Grand opening
06:15 First power up
07:40 The incredible principle of operation (with elevator music)
13:25 Our instrument has unexplained HP mods!
15:46 Did we just get the flying clock model?
19:08 Reverse engineering the second mod
21:59 Supporting evidence from HP doc
22:49 We understand it now, should be repairable