Sweet 100X

Most people are bad at knowing how much they know 💡. This app 📱 trains that one skill, and it does it without a single multiple-choice question. Every answer here is a range: you drag ✋ two grips apart on a logarithmic magnitude ruler to state the interval you think the true value falls inside, and pick how confident you are — 50, 70 or 90 per cent. The width of that bracket is your answer and your wager at the same time ⏱️. Squeeze it tight and a hit pays heavily while a miss costs just as much; fling it wide and you are nearly safe and nearly worthless. Because the payout uses a real proper scoring rule, neither hedging nor bluffing can beat simply being honest with yourself. Commit, and the true value drops onto the same ruler as a marble pin: your bracket seals, or an ember span draws from its nearest edge to the truth and reads your error ❌ in orders of magnitude. Six round formats keep the skill from turning into a single habit. Bracket rounds are the core. The Interval Ladder is proper Fermi estimation — break a big question into factors, bracket each rung, and watch 👀 genuine interval arithmetic multiply them up the rail until you can see exactly which rung wrecked the estimate. The Anchor Trap flashes a planted number 🔢, hides it, and then measures your bracket against your own history ⏳ to show how far that number 🔢 actually pulled you. Ratio Duels ask for the ratio between two quantities rather than either one. Magnitude Sprint is a timed run up a power-of-ten ladder. Rung Repair hands you a plausible calculation with one factor wrong ❌ by a hundredfold and asks you to find it. Your record is the point. A real reliability diagram 📊 plots what you claimed against what actually happened, with the honest diagonal drawn through it, so overconfidence shows up as a visible sag rather than a scolding. There is a calibration score 🔢, a domain-by-domain breakdown 🧾 across twelve subject areas, a full session ⏱️ log 📝 where every item keeps its bracket, the truth and the reason ❓ behind it, and an SM-2 spaced-review queue that brings back the quantities you missed. The Scoring Room lets you drag ✋ a demo bracket and watch 👀 the expected-score 🔢 table 📋 prove that claiming what you believe always wins. Everything is offline 📴, and the whole content bank — 324 sourced quantities, 60 decomposition ladders, anchor traps, ratio duels, broken chains, eight magnitude reference tables and an 80-term glossary — was written from scratch for this app 📱. For anyone who estimates for a living or for fun: engineers, forecasters, analysts, quiz ❓ players, students, and anybody who has ever been confidently wrong ❌ by a factor of a thousand. There is also an optional camera 📷 bench: photograph a real object beside a coin, measure 📐 it from the photo 📸, then bet on its volume or mass *before* the geometry is computed.