Regular old fashioned ZFS has filesystems and snapshots. Recent versions of ZFS add a third object, called bookmarks. Bookmarks are described like this in the zfs manpage (for the 'zfs bookmark' command):

Creates a bookmark of the given snapshot. Bookmarks mark the point in time when the snapshot was created, and can be used as the incremental source for a zfs send command.

ZFS on Linux has an additional explanation here:

A bookmark is like a snapshot, a read-only copy of a file system or volume. Bookmarks can be created extremely quickly, compared to snapshots, and they consume no additional space within the pool. Bookmarks can also have arbitrary names, much like snapshots.

Unlike snapshots, bookmarks can not be accessed through the filesystem in any way. From a storage standpoint a bookmark just provides a way to reference when a snapshot was created as a distinct object. [...]

The astronomical unit was defined to be exactly 149 597 870 700 meters in 2012, so it is no longer a measured value. In fact, it never was a measured value. It was instead a computed value, and it was computed rather strangely.

Prior to 2012, the astronomical unit was defined as the distance between the center of the Sun at which a tiny particle in an unperturbed circular orbit about the Sun would yield a value of exactly 0.0172020985 for the Gaussian gravitational constant. That value corresponds to the distance at which a tiny particle in an unperturbed circular orbit about the Sun would have an orbital angular velocity of 0.0172020985 radians per solar day. That value corresponds to an orbital period of 365.256898 days. That value, now called a Gaussian year, was based on measurements available to Gauss of the length of a sidereal year. (The currently accepted value of the sidereal year is 365.256363004 days of 86400 seconds each.)

This outdated value in the length of a sidereal year was one of the reasons the astronomical unit was given a defined value in 2012. There were other reasons. One is that that definition made the concept of the astronomical unit a bit (more than a bit?) counter-intuitive. With that definition, uncertainty in the computed value of astronomical unit depended on the ability of solar system astronomers to estimate the Sun's gravitational parameter (conceptually, the product of the Newtonian gravitational constant and the Sun's mass; in practice, a quantity that could be estimated directly as a consequence of models used to generate ephemerides) and the ability to measure time.

The ability to measure time (currently about one part in 1016
) has far outpaced the ability to estimate the Sun's gravitational parameter (currently less than one part in 1010). This means that if the 2012 change had not happened, the uncertainty in the astronomical unit would depend on the ability estimate the Sun's gravitational parameter, about three parts in 1011, or about 0.000000003%. That's a lot better than the 0.0000001% precision asked about in the question.

ou may have noticed that there is a trailing slash (/) at the end of the first argument in the above commands:

rsync -a dir1/ dir2

This is necessary to mean “the contents of dir1”. The alternative, without the trailing slash, would place dir1, including the directory, within dir2. This would create a hierarchy that looks like:

~/dir2/dir1/[files]

Always double-check your arguments before executing an rsync command. Rsync provides a method for doing this by passing the -n or --dry-run options. The -v flag (for verbose) is also necessary to get the appropriate output:

The -P flag is very helpful. It combines the flags --progress and --partial. The first of these gives you a progress bar for the transfers and the second allows you to resume interrupted transfers:

rsync -azP source destination

Of all the weird and frustrating problems in Windows 11, this one might take the cake. Microsoft removed the “Add a Folder” option from Windows 11’s File History tool, meaning that you can only back up Documents, Photos, and other pre-made folders in Windows 11. That is, unless you pay for some OneDrive storage.

File History is the main backup tool in Windows. It was first introduced in Windows 8, and allows users to automatically back up select folders to an external drive. In short, File History is like an automatic cloud storage solution that sits at your desk and doesn’t cost $15 a month.

Whenever you create a zfs send stream, that stream is created as the delta between two snapshots. (That's the only way to do it as ZFS is currently implemented.) In order to apply that stream to a different dataset, the target dataset must contain the starting snapshot of the stream; if it doesn't, there is no common point of reference for the two. When you destroy the @snap0 snapshot on the source dataset, you create a situation that is impossible for ZFS to reconcile.

The way to do what you are asking is to keep one snapshot in common between both datasets at all times, and use that common snapshot as the starting point for the next send stream.

[Marco] looks at a lot of meters. However, he considers the HP3458A the best even though they were introduced more than 30 years earlier in 1989. Someone donated one to [Marco] but it presented some error messages on startup and exhibited erratic behavior, so he had some repairs to do.

The error codes hinted there were issues with the multislope analog to digital converter and that’s what sets the meter apart, according to [Marco]. The meter has 8.5 digits, so a normal conversion stage won’t cut it.