eroux

Supplying an <a href="https://en.wikipedia.org/wiki/International_Standard_Book_Number" rel="nofollow ugc">ISBN</a> (and, optionally, a Title) will display a cover image of the relevant book with a link to that book’s page on <a href="https://books.google.co.za/" rel="nofollow ugc">Google Books</a> using the Google Books API.
Using the Widget you can choose whether to:
<ul>
<li>Force all calls to Google to be HTTPS, instead of the API returned HTTP</li>
<li>Pad the Image (selected by default, uses internal CSS)</li>
<li>Display a Box-Shadow (selected by default, uses internal CSS)</li>
<li>Choose Alternate Google Country (defaults to “Worldwide”)</li>
</ul>
as well as
<ul>
<li>Decide whether you would like to use a Title</li>
<li>Define the ISBN-10 or ISBN-13 of the book.</li>
</ul>
<h3>Usage</h3>
<ol>
<li>Activate the Plugin via “Plugins” → “Currently Reading” → “Activate” (if you hadn’t already done so).</li>
<li>Go to “Appearance” → “Widgets” and drag the “Reading” widget into whichever Sidebar you choose.</li>
<li>In the “Currently Reading” widget, you can then customise it further.</li>
</ol>

Currently Reading

Displays a cover image of a book with a link to Google Books based on a supplied ISBN-10 or ISBN-13.

Joeri van Veen

The reading progress bar is a great user experience on longreads. Especially if it accurately depicts the reading progress in the article text, and nothing else. This is standard on single blog posts and enabled by default.
Customization:
<ul>
<li>
Location top of screen, bottom of screen or below a sticky menu.
</li>
<li>
Choose color of the reading progress bar.
</li>
<li>
Have the bar start at 0% even when part of the article is visible.
</li>
<li>
Select post types you wish the bar to appear, or individual posts.
</li>
</ul>
Behaviour:
<ul>
<li>
The reading progress bar has smooth initializing since part of the text may already be visible, after that a lightweight update-function ensures quick response while scrolling.
</li>
<li>
The bar can attach itself to any (sticky) element that you define as an admin, when there are multiple, the first visible element will be used.
</li>
<li>
When there is no (longer a) visible element to attach to, the bar displays at the top.
</li>
<li>
If there is no single article identified (by class names or id) it uses the whole page to calculate progress.
</li>
</ul>
Estimated reading time (beta)
Since 1.6.0 this plugin has rudimentary estimated reading time functionality, for when your theme does not support it out of the box. 
There are some potential issues, some of which cannot be fixed in a plugin. If it does not work for you, switch it off. It will have no effect on the plugin then.
This is my 6th WordPress plugin but my first one freely available to everybody. I hope you enjoy using it as much as I enjoy building it!
Regards, 
Joeri

WP Reading Progress

Light weight fully customizable reading progress bar. Sticks to top, bottom or sticky menu, with fallback for small screens. Includes ert (beta).

Currently Reading vs WP Reading Progress