Ballpark

Ballpark helps you make rough calculations quickly. Instead of exact answer, the idea is to get an approximate answer (within + or - 10% range of the right answer). This is the base requirement for being good at guesstimation.

BallPark is a completely offline-first app. There are no logins, no servers, and no distractions. All your progress is stored locally on your device. It’s designed to be your private, focused training ground.

Features

• 12 Problem Types: Addition, Subtraction, Multiplication, Division, Percentages, Ratios & Fractions, Reverse Percentages, Growth Rate, Compounding, Breakeven, Weighted Average, and Scaling & Conversion
• Customizable Settings: Adjustable precision (5% or 10%) and time limits (3 or 5 minutes)
• A Keypad Built for Speed: Fumbling with a standard keyboard is slow. Our custom keypad includes shortcuts for Thousands (K), Millions (M), and Billions (B), so you can input large numbers like “$17.5M” in a fraction of the time.
• Real-time Performance Tracking: Live scoring and timer
• Detailed Analytics: Performance charts and statistics with genre filtering
• Cross-platform Support: Works on desktop, mobile, and web with keyboard and touch input
• Data Persistence: Session history and performance tracking

If you are interested in installing it on your android phone, then you can get the APK file here.