No, it isn't. There's a reason that Schroedinger's cat and Wigner's friend and "the measurement problem" are a thing. (And see my last comment below.)
> Stern-Gerlach experiment.
The basic SG experiment setup has two components: the magnets, and a pair of detectors. When you compose multiple SG experiments you compose only one of these, the magnets. The detectors are all moved to the END, AFTER the electrons have transitioned all the magnetic fields. So you are not actually measuring the positions of the electrons at the intermediate stages, only at the end, and only once.
So no, the SG experiment is NOT an example of making two successive measurements on the same particle. Go back a re-read what I originally wrote:
> The best you can do is run a particle through a series of filters and look at where it ended up. You can then retrodict that the particle went one way or went another way, but you cannot actually measure its trajectory. In fact, you cannot even know that there even is a particle in your apparatus until the end when you actually measure it.
In the SG experiment, the magnets are the filters. You will find that ALL quantum experiments have the same constraint.
(BTW, the actual term used by physicist is "preparation". You can use multiple SG magnets in series to PREPARE your quantum system, but you can only actually MEASURE it once. Once you measure it, the wave function collapses, and you no longer have the same system.)
> Have you considered the double slit experiment, where the whole point is the difference in length of trajectory?
Yes, of course. You appear to have completely missed the point. The path-length difference in the experiment I pointed you to is orders of magnitude larger than the standard two-slit experiment. That matters.
> if you bloop spin twice
What does it mean to bloop something? You will find that you will have no more success in defining "bloop" than physicists have had in defining "measurement". Here's a hint: are bloops/measurements reversible?