Singular and past tense...Chuckle, yes seer stones is correct not the seer stone singular..... neither one of you understand meanings....
Plural: more then one. Like the stones in the Brest Plates or spectacles. Totally embarrassing for you guys.
"During the translation of the Book of Mormon, Joseph Smith apparently used both of these instruments—the interpreters and his seer stone—interchangeably."
"These two instruments—the interpreters and the seer stone—were apparently interchangeable and worked in much the same way such that, in the course of time, Joseph Smith and his associates often used the term “Urim and Thummim” to refer to the single stone as well as the interpreters."
Here it is plural...because it associates the Interpreters...which are two stones with the single egg-shaped stone.
...."And Joseph used these: the Urim and Thummim, seer stones, in the hat...."
The Book of Mormon Is Tangible Evidence of the Restoration
President Russell M. Nelson and Jean B. Bingham, Relief Society General President, discuss the translation of the Book of Mormon at the site in Pennsylvania where Joseph Smith translated it.
www.churchofjesuschrist.org
Also...Singular, present tense.
... "Featured in the new volume are photographs of a brown seer stone likely used by the Prophet Joseph Smith in his translation of the Book of Mormon. ..."
Book of Mormon Printer's Manuscript, Photos of Seer Stone Featured in New Book - Church News and Events
A new volume of the Joseph Smith Papers project featuring the printer's manuscript of the Book of Mormon was released August 4 by the Church Historian's Press, an imprint of the Church History Department.
www.churchofjesuschrist.org