So where is the sample rate and how do you set it?

The 3 core settings for successful FFT are the timebase initially to have many periods on the display, the Start/Center/Stop frequencies and the FFT points for speed of FFT refresh.
Knowing the fundamental frequency helps us make revealing settings so to display several harmonics we need set a center frequency of 2 or more times the fundamental.
Initially playing with FFT of the 1kHz probe compensation output lets us get the feel of making good FFT settings which we can apply to other real frequencies of interest however always the fundamental guides us how to make good settings.

Quickly, we already know the compensation output is 1kHz and to display this at the 1st graticule set a center frequency of 5kHz (3rd harmonic) and a Hz/div setting (horizontal scaling) of 1kHz/div. Square waves harmonics rise every odd fundamental multiple whereas sinewave harmonics rise every even fundamental multiple.

1000X-E series Siglents all offer 1Mpts FFT and to process all those can take some time and we don't always need such detailed FFT so we can reduce FFT points lower to speed processing and FFT sweep.
Often 128kpts is plenty to get adequate results. The FFT box on the display tells us how many are selected and in the case of the images you posted there are 1048576 = 1 Mpts.

 

https://support.ircam.fr/docs/AudioSculpt/3.0/co/FFT Size.html

FFT Size
The window size influences the temporal or frequency resolution, or precision of the representation of the signal. The frequency resolution can be increased changing the FFT size, that is, the number of bins of the analysis window.

The FFT length/size determines the number of bins (frequency filters). The bin (the equivalent to a analog narrow band filter) width is the resolution bandwidth.

 

Slightly OT but what's a recommended replacement fan for this scope? At power-up the fan sounds like a old tractor engine starting in dead winter. After about 30 seconds of rattle it smooths out, suspect the 'bearings' are toast. I'd like a fan with 'real' bearing, not sleeve.

 

Slightly OT but what's a recommended replacement fan for this scope? At power-up the fan sounds like a old tractor engine starting in dead winter. After about 30 seconds of rattle it smooths out, suspect the 'bearings' are toast. I'd like a fan with 'real' bearing, not sleeve.

Same as OEM.
Fan failures are rare.
FYI these use a different and slightly quieter fan than the 4ch X-E's.

 

Slightly OT but what's a recommended replacement fan for this scope? At power-up the fan sounds like a old tractor engine starting in dead winter. After about 30 seconds of rattle it smooths out, suspect the 'bearings' are toast. I'd like a fan with 'real' bearing, not sleeve.

My fan is also doing this, but in reverse. I’d already lubricated it once but now it is slightly noisy running but a slight shock to the case can set it off producing a lot of noise. If I shut it off and let it cool down (I surmise that the bushing expands, allowing the rattle) it will run fine indefinitely until the next time I move it a little.

I figured I would just replace it this time.

 

My fan is also doing this, but in reverse. I’d already lubricated it once but now it is slightly noisy running but a slight shock to the case can set it off producing a lot of noise. If I shut it off and let it cool down (I surmise that the bushing expands, allowing the rattle) it will run fine indefinitely until the next time I move it a little.

I figured I would just replace it this time.

(Mine is a 1204X-E)

 

Same as OEM.
Fan failures are rare.
FYI these use a different and slightly quieter fan than the 4ch X-E's.

What's a fan model number I could use as a reference for a 'better' fan for the 2ch model.

 

(Mine is a 1204X-E)

As mentioned these are a different fan to the 2ch models.
We did some investigations for quieter fans but found Siglent engineers had selected the best unit available. Even a Noctua replacement a customer selected wasn't as quiet.
I have replaced only one in a near new 4ch X-E under warranty and Siglent were very interested as they at that time had not had problems with this model fan.

BTW I removed the metal grille to attempt to reduce noise with only a slight improvement.

SDS11/1204X-E OEM fan:
CD-FAN
DFM6025S
12V 110mA 2 wire

 

What's a fan model number I could use as a reference for a 'better' fan for the 2ch model.
View attachment 304774

I would attempt to match OEM especially to get a low noise fan and with some effort you can often read the fan model # through the grille without disassembly.
Currently I don't have a unit unpacked but might be able to supply this info in a day or 2.

 

I would attempt to match OEM especially to get a low noise fan and with some effort you can often read the fan model # through the grille without disassembly.
Currently I don't have a unit unpacked but might be able to supply this info in a day or 2.

Thanks. Searched around and found a long lifetime (noise is not a prime factor) replacement fan for mine and a few work units.
https://www.mouser.com/datasheet/2/120/ebm_papst_600N_rev2016-1880389.pdf