Web Storage (formally known as HTML5 sessionStorage and localStorage) is a feature that's been added to recent releases of most web browser software (Safari, Edge, Google Chrome, Firefox, etc.).
What Is It?
Specifically, web storage allows web developers to create web apps that can store data to the user's web browser for later recall. This means data is stored on your computer and it can only be accessed by the website where the saved data originated from (similar to "cookies").
Limitations and Drawbacks
Storage Limit: Each web browser limits the amount of data that can be stored by any one website (5-10MB), and no visual cues are displayed once that quota has been exceeded. Therefore it's important to periodically clear stored data you no longer need.
Can't Be Shared Between Devices: Saved data can only be accessed from the same device and web browser it was stored in. For example, if you save a set of calculator entries to Google Chrome on your desktop, you won't be able to recall it from your mobile Safari on your iPhone.
Lost Data Cannot Be Recovered: If you upgrade your web browser, buy a new computer, inadvertently clear your web browser's web storage, etc., there is no way to recover your data. Therefore, if the saved data is important to you, always keep a hard-copy of your printed calculator results, or backup your data to text file on your computer (instructions on Data tab of each calculator).
Support Not 100%: Some web browsers still don't support web storage (Opera Mini for one), and storage may not work while in Private Browsing mode.
Solution to Limitations and Drawbacks
If you subscribe to the Ad-Free Cloud Version of the website, your data is stored in a secure online database, which can be recalled from any device or web browser, doesn't rely on web browser support, has no storage size limitations, and the odds of recovering lost data are much higher (web host backs up database).