"You can't put one on your bedroom door and hide from your parents. As soon as they wanted to find you they'd want to find your bedroom by necessity. That would let them force their way pass the Hiding Stone's ability. Like I said it isn't incredibly strong or anything, it just makes things less noticeable." Harry explained getting a pout from Tonks which caused Penny and Harry to laugh slightly. Leading the girls into the workshop Harry quickly grabbed a few thin planks of wood he'd managed to make from wood Hagrid collected from the Forbidden forest. It annoyed him that he still needed to use his wand to use the Cutting Charm with any precision; wandlessly it was always overpowered and sliced the wood through completely. With four small planks chosen Harry set about carving the self-destruction sequence Ollivander had passed on to him. He used some glue to stick the planks onto all four sides of his Test Frame so that the two runic sequences came into physical contact which primed the self-destruction sequence. If anyone attempted to pull the wooden planks off the edge of the stone frame the self-destruction sequence would activate and destroy both sets of runes. A quick spell to instantly dry the glue was provided by Penny and Harry picked up the Test Frame and walked out of his hidden workshop with the girls. Harry had Tonks and Penny put their hands on the Hiding Stone as he placed it back on the door handle. The three watched the stone glow briefly before it stopped and Harry grinned when he noticed that both girls could still notice the door normally.
"Did the two of us touching the stone make it exempt us from its effect?" Penny asked curiously as she looked at the door with the trinket on the handle.
"Yes, the Hiding Stone doesn't affect the one who placed it. Since all three of us placed it on the door you two are now the only other people that will notice this door normally. You won't be able to get in without me unless you knock down the door though. But you'll know where to look for me if you need to find me." Harry explained with a smile. Both girls smiled back at Harry happy that he was willing to bring them into the know about his secret workshop. The trio quickly made their way back to the Great Hall and quickly realized that everyone was still there waiting for Harry to speak.
"You'll do fine Harry, just take a few questions and it'll be over soon." Penny encouraged.
"Yeah, I bet most of them just want to know their own reading, so you'll just have to give them their numbers." Tonks grinned.
"Thanks you two." Harry sighed as he walked to the front of the Great Hall when Dumbledore motioned for him. Standing in front of the whole school was a bit nerve wracking but Harry swallowed his nervousness and began this impromptu presentation.
"You may begin whenever you feel ready, Mr. Potter." Dumbledore gave him the go ahead.
"So as you all know from the Prophet today I'm a bit of a burgeoning Enchanter. My first professionally sold item is called a Scouter." Harry started off while pulling out his Scouter. "This lens when focused on a Wizard or Witch will give me a reading on their total amount of mana, which is a term I use for Magical Energy. The more mana a Magical has the stronger they are from a magical standpoint." At that a few hands were already raised and Harry picked one near the back. "Yes, the Hufflepuff in the back, you have a question?"
"Yes, my name's Forrest Prott, I was wondering how you decided to actually measure Magic? No one has ever agreed on an accurate way." Forrest asked which prompted another four hands to lower as he had apparently asked their question.
"I used the Lumos Charm as the base. I just kept using less and less mana to cast it until I found out the absolute minimum amount required to get the spell to work." Harry answered the same way he'd answered Tonks back on the Hogwarts Express. "I then designated that bare minimum as equal to one unit of mana. As far as I'm aware that is the least amount of mana that can produce a successful spell."
"Oh, that makes sense; I see how that works out for measurement." Forrest nodded before sitting back down. Harry looked around noticing the hands still raised, he picked one close to the front this time. "The Slytherin in front, what do you want to ask?"
"My name's Emilia Hawthorn, I'll just ask what most everybody is probably going to ask anyway. Can we get our own mana, as you call it, measured today?" Harry noticed almost every hand lowering at Emilia's question.
"That's why I brought this." Harry replied as he held up his Test Frame. "This is the next product I plan to sell after I make enough of them. I call it a Test Frame. It's a talisman that allows a person to measure their own mana by holding it and pushing their mana into it like you would your wand." The excitement in the room increased dramatically and Harry watched it spread on all the student's faces. He turned back to look at the Head Table before making an offer. "If you'd like I'd be willing to make one for each of the Hogwarts Houses. They could be kept in the Common Rooms so that any student can measure their mana whenever they'd like." All of the Professors smiled at Harry's offer. Barring Snape, who never smiled, and Quirrel who was still twitchy and looking around nervously.