Ok I know this sounds little strange for an electronic gizmo, but I've had for 10 years, the same color calibrator. There are newer ones out there, but for a device that I literally use once a year, it seems sad to have to buy a new one. This is the Spyder3 and about three years ago, DataColor discontinued support for it. So my monitors have not been calibrated for a long time.

There is an open source project called DisplayCal which dispenses with the proprietary software, but for the last year, every time I've tried to use it with the Spyder3, it has crashed. Well, with all this pandemic isolation time on me, I've been fixing the house and thought I'd give it one last try before trashing the Spyder3 and getting a new calibrator (more on that below).

When it suddenly all started working. So here are notes on how to make an old Spyder3 work with DisplayCal:

1. Installation is easy with brew install displaycal which is great!
2. First of all, there are no real instructions for this as it's a pro tool. So when you get the first screen, it will ask you about downloading. So first plug in the Spyder3 to your Mac and it should detect it and download some software.
3. Now it asks whether you want a black background. Make sure to select no, otherwise you can't see the calibration menus. I really got stuck on this as the window is behind the black background. If you have multiple monitors, then make sure to move that window away before starting.
4. The startup time is long like a minute, so be patient, but eventually, it should have a dialog with a button that says Start Measurement the point here is to get your monitor roughly right. It then will show a grey color swatch and you click.
5. The most important thing is actually at the bottom which is the light output. The thing is constantly taking measurements and emits a click sound. You need to set the brightness of your monitor to the right level. It is confusing because the top part which about targets and you want to get Red, Green and Blue in the center. But the bottom is not. The arrow is just what you had it first set at and gives you the brightness measured in Cd/m^2 (don't ask, but this is candlepower per square meter).
6. Here you have to manually figure out how bright you want things. If you are doing prepress, then you want it at 80-120 and the room should be dark. I have previously calibrated this, but you need to know the right brightness. If you are doing this is a daylit (but no direct sunlight!) room, then you set it higher at 140-160Cd/m2. We have a few rooms, but the dark rooms we set for 120 and then if there is a skylight for 160. For our MacBooks, we set to 150 because they could be in daylight and you have to remember the brightness settings. For a MacBook 2017, 150 is 7/0 clicks.
7. Now comes the laborious process of getting your monitor close to the right color. Every monitor is different, but for an ASUS, typically, you need to find a setting that is basically "User" mode. On older monitors, this is just labeled User but in later ones, you need to find a setting like Standard that let's you do manual settings. Some of the modes like sRGB for instance lockout the color controls.
8. What you do now is this strange dance of changing the color settings, waiting for the DisplayCal to show you want it thinks they are and then you have the right initial start. I would definitely do a label makers and put it on the display what the Brightness, Contrast, Hue, Saturation and RGB Gain on so if the monitor resets you don't lose this.
9. Then when you are done, you hit Calibrate and it spends about an hour taking color samples.
10. In the end, you get a new color profile that you can save and then use!

New Color Calibrator

If you don't want to recycle or don't have one, then if you are a photographer, I highly recommend a kit that does both monitor and printer calibration.

Otherwise, your prints are going to be way off, there are really only three vendors left who do this which are X-rite Colormunki/i1Display and and the DataColor's They each have a huge line of products from $100-500 (someone in marketing has taught them how to value maximize). So most reviews like Just Creative are really going through them all and figuring out what the best the way to look at this is that the three products are all about the same. One review said the Colormunki was higher quality as an aside, but here's the decoder ring for each Datacolor SpyderX They use the same sensor for everything and the actual costs are the bundled software and other devices. Tl;dr. Get the SpyderX Studio if you are serious about monitor and printing accuracy. There are two monitor calibrators called the SpyderX Pro for$170 and then the higher end SpyderX Elite for $270. The two look identical to me physically and one site said that the only difference is software. If you are going to be using DisplayCal, you might as well just get the cheap one and not pay more for their software. So the SpyderXPro is the value leader They also have bundled packages as well such as the most interesting is the SpyderX Studio which includes printer profiling for$500 called the SpyderX Studio. This color-matching at the paper level definitely makes a difference, so if you are printing at $500 it's expensive but definitely worth it. This is their latest line, the Spyder5 are their older ones, so get the SpyderX if you are buying new. X-Rite i1 and Colormunki They have two product lines, the i1 (for enthusiasts) and Colormunki (I almost want to get this one because of the name but this is their beginner line). i1Studio for$489 at Amazon. This is unique in that it is both a monitor and ink jet printer calibration in a single device. You can even use it to calibrate an iOS screen (mainly for photographers who are doing proofing at a shoot I think). And it supports projector profiling. It's actually a rebranding of the old Colormunk Photo.

X-rite i1DisplayPro. I've got to say the name they give these things is pretty ridiculous, but at \$260, this is comparable to the SpyderX Elite and of course it doesn't have printer calibration.

They also have a licensing deal with Pantone, so you will see their stuff sometimes marketed as Pantone Colormunki but it is really X-rite that makes it.