@dor123 , have you tried the spectrometer with single wavelength light sources? See if the reading on the spectrometer matches with the actual wavelength. For example, a red laser is ~650nm, a green laser is ~532nm, a violet laser is ~405nm, a neon lamp has a peak at 632.8nm. If the values for these are close (+ or - a few nm) then the spectrometer should be correct.
(Don't point the laser directly on the spectrometer, point the lasers on a white wall and place the spectrometer pointed towards the wall looking at the laser dot.)

There is no calibration instructions in the manual.
"Note: The calibration function is restricted to use by metrology institutes only and is prohibited for use by
non-professionals."

If im not wrong, your spectrometer is model LS335. If its of any help, try downloading the manual for it here.

Ask the seller, they are often helpful

I don't know how to calibrate this spectroscope.
@RRK, @James, can you help me?

For the wet sponge vs brass wool:

The wet sponge is softer, so less abrasion to the tip, but it cools it rapidly, creating heat shocks. So when still generally acceptable for lead soldering (where the temperatures use to be in the 300degC ballpark), the higher temperatures required for lead free means the shock becomes way more significant problem. Plus if the tip is not hot enough to evaporate the water instantly (when someone is wiping the tip when it is already cooling down - never do that), it promotes corrosion of the iron layer.

The brass wire wool is a bit harder, but still should be softer than a good quality tip, but it does not thernmally shock it. For higher temperature lead free soldering (around the 350degC tip) this becomes very important.

Good quality tips use way more than 2 or 3 layers, usually the copper body is coated with Ni (via some intermediate) to get hard, strong surface, mainly at the high temperatures, with iron coating on top of it to form a  layer easilly wettable with molten solder. Nickel alone forms rather hard oxide layer on it (that normally is what protects it against further corrosion), which makes it hard for the solder to adhere to.

So in other words quite complex structure for any DIY.

The "900" style is so common, you can find all kind of tips for it, from really bad garbage till really good quality, obviously more expensive, ones.
Don't forget this format has its origin as a rather good quality and also not that cheap stations, so good quality tips are still made for it.
Only because it became a format chosen for cheepeese clones, the market is also flooded with garbage quality product offerings you have to dig through...

Over the past two years, we have replaced 4 EOL bulbs. All four bulbs are LED bulbs, but there is a significant difference in their lifespan. The bulb with the longest lifespan was installed in early 2017 and worked normally until the beginning of last year. Calculated based on a daily usage of 4 hours, it has used for approximately 12,000 hours before EOL, exceeding the nominal lifespan of 10,000 hours. The bulb with the shortest lifespan is a Philips CRI 90 10W bulb manufactured by Signify. It was installed in March 2025 and was used for five hours every day. It EOLed in October of the same year and only worked for about 1,000 hours, which is the worst bulb I've ever used (Even worse than any of the CFLs and Incandescent lamps used in my home). After that, I replaced both of the mentioned bulbs with the same Philips CRI 90 bulbs. However, after only three months, the color of the light from these two bulbs became visibly different. This is sufficient evidence that the Philips bulbs currently sold in China have very poor quality. I will no longer purchase any Philips LED bulbs for installation in my home in the future. Fortunately, there were no EOL fluorescent lamps in my home in the past two years. Most of them will be replaced with LED modules customized by me this year, and the removed tubes and ballasts will add to my personal collection.

Maybe you need to calibrate it? Use a light source with known wavelength (either lasers or gas discharge lamps) to calibrate the spectrometer. Keep in mind don't point lasers at the spectrometer directly, point it towards paper.

Took some Creatine and got some weightlifting in earlier in the day, then got some pizza from Dominos as a protein meal, followed by a protein shake. (Vanilla muscle milk protein shake is the best.) 8 out of 10 for the pizza, as usual... 9 out of 10 for the protein shake.
Also... off topic... I'm beginning to notice the high view count this topic has been getting... I know there are a lot more members on LG compared to way back in the day when I first joined in 2010, but... who's viewing this so much? Bots?

There were also gramophone lamps. http://www.douglas-self.com/MUSEUM/COMMS/oddgram/oddgram.htm#lampRead the whole page too if you want, and also just look at the whole Museum of Retrotech on his site. This Self person is cool.