Tell us about yourself!
For Dry Erase white boards: Just rub a Dry Erase marker back and forth across the permanent marking and the solvent will usually remove it. (If permanent marking is left too long it will make an indelible stain.)
The Oughtred Society (Slide Rules) just published the English translation of Curt Herzstark's Autobiography.http://www.oughtred.org/curta-book.shtml
This is mine (original) which was purchased for $10 during the early1980s, with no instruction manual. I can tell anyone how to Add, Subtract, Multiply and Divide using the device.
Flea Market in Santa Cruz, California. I knew exactly what it was, but still tried to get the seller to lower the price below $10! (~$850 on eBay today) It took me about a month of intense research in a university library to figure out the 4 math functions, as there was no Wikipedia... :-)
Raspberry Pi Class
What You'll Need & Learn