The concept of an HLC was invented in this 2014 paper, to combine and preserve the convenient features of both physical and logical clocks:
"Logical Physical Clocks and Consistent Snapshots in Globally Distributed Databases" by Sandeep Kulkarni, Murat Demirbas, Deepak Madeppa, Bharadwaj Avva, and Marcelo Leone.
https://cse.buffalo.edu/tech-reports/2014-04.pdf
See for instance their use in CockroachDB and MongoDB as alternatives to Spanner's TrueTime approach when atomic clocks are unavailable.
https://cse.buffalo.edu/~demirbas/publications/augmentedTime.pdf
https://github.com/AugmentedTimeProject/AugmentedTimeProject
https://muratbuffalo.blogspot.com/2025/01/use-of-time-in-distributed-databases.html
Enjoy,
Jason