The Zone Gradient is a Photoshop Plugin which is designed to be used as a visual reference as it shows both the Lightness values and also the corresponding zones for a particular shade of grey.
The Plugin has been designed to work across the three main working colour spaces, sRGB, Adobe RGB 1998 and ProPhoto RGB.
When the Zone Gradient panel is used used in conjunction with the Photoshop Info Panel, we can very quickly place anchor points anywhere on the image and then see the values of the tones beneath the curser.
With this information, we can then use the Zone Gradient panel to visually inform us of what particular zone the anchor point falls into.
I use this on a daily basis and find it to be a handy addition to my workflow. The Zone Gradient Panel is compatible with Photoshop CC 2020 and above for both Windows and Mac operating systems.
Photoshop version 22.0 or newer
After downloading the file, unzip it to your desktop and then double click the enclosed ccx file and then follow the on-screen instructions.