Antique "Indu" Spirit Writing Slate

 So the Item is very unique, and I am unable to find any information or anything like it online.  It is an "Indu" Spirit Writing Slate.  Yes I said "Indu" Not Hindu.  I have always had a facination with items like this, and this is the first time I have ever seen anything like it.  I do know that back in the day it was more common place for spiritualist and upper class to hold seances and try to communicate with the dead.  I also know that Mary Todd Lincoln was known to hold seances like this after the death of her son.  From what I understand the Spirit writing slate like the one in the pics below were exactly what was used during that time.  I know that they found that most of the psychics and mediums of the time who used and item like this were frauds, but I do not believe that makes this piece any less significant or less unique.  I am kind of thrown off by the price.  Initially I would have thought of this like a toy, but simply not sure.  That being said a price of 75 cents would indicate to me that it is probably around 1920s, but I really have no clue.  Overall the condition it not bad.  The original direction pages are old and brittle, but they are relativley in tact and you can still read what it says.  Yes there are pieces missing, but nothing that would effect it's readability.  The slates are in great condition, with a wood frame that has a cloth lining around them with twine.  The original piece of twine is still on the slates to tie them together.  I got brave and opened it up.  Again the slates are in great condition. Initially I thought they were chipped and then I realized that the chippings i see are from the original slate pencil.  From my understanding when they would use a board like this they would break the slate pencil into many smaller pieces, then tie the two slates together.  This was suppose to give the opportunity for spirits to communicate.  At least that is what I understand of how it worked.  I could be misinformed. Over all the piece is very old and when it comes to the attached pages.. they are brittle.  That being said, I am just in awe that I am unable to find any information about this item anywhere.  I could really use your help.  Maybe a year, and hopefully a value.  Thank you.