Handspinners! Yarnaholics! Fiber addicted!
If you have an iPhone or an iPod Touch, go immediately to the iTunes App Store: the iSpin ToolKit for iPhone and iPod Touch has been finally released!
This is the first app for handspinners.
It’s a dream! It is the app I was waiting for.

Look at what it contains:
• Twist Angle Finder: Lay your yarn over the screen and swipe until the lines on the screen to match the angle of your twist. Can be used for singles or plied yarns.

• WPI Gauge: Lay one strand of yarn over the screen and scroll until you find a stripe that matches the width of your yarn. For very fine yarns, wrap around the iPod five times. Can measure anywhere from 2 to 100 WPI.
• TPI Gauge: Hold your yarn over the square and count the bumps to determine the twists per inch. For singles, let the singles self-ply, count the bumps, and divide by 2.
• Rulers: Full screen inch and centimeter rulers.
If this is not enough for you, consider that iSpin ToolKit contains 13 calculators:

• Project Estimator : How much fiber do I need to spin the specified yarn?
• WPI to Approximate Grist: Converts from wraps per inch to yards per pound.
• Grist Converter: Converts between yards per pound, yards per ounce, meters per kilogram, meters per gram, and even miles per pound and kilometers per kilogram.
• Niddy Noddy Calculator: How long is the yarn I wrapped on my niddy noddy?
• Simple Balanced Yarn TPI from Singles: I have two singles spun to 20 TPI, how much twist should I apply to make a balanced yarn?
• Singles TPI from Desired Yarn TPI: I want a plied yarn of 8 TPI, how much twist should I put into the singles?
• Singles WPI from Final Yarn WPI: I want a plied yarn of 22 WPI. What should the grist of the singles be?
• Plied WPI from Singles WPI: I have singles of 18 wpi. What will its plied grist be?
• Fiber Weight to Singles WPI for Length & Plies: I have 7 ounces of fiber, and I want 2,200 yards of 2-ply. what should the grist of the singles be? What will the plied yarn’s WPI be?
• TPI from Wheel Configuration: Given my wheel ratio and how many times I treadle for my draft zone length, how much spin am I putting into my yarn?
• # of Treadles for Desired TPI: How many time should I treadle for a given draft zone length and a given wheel ratio to get my desired TPI?
• TPI for Firmness Calculators using either the Mabel Ross or the Alden Amos Method: These calculators use two different methods to determine the final yarn’s TPI based on the desired WPI and firmness of the final yarn. (soft, medium, firm, etc.).
Each calculator includes instructions and the formulas used for each method.
iSpin Toolkit also includes a reference section that discusses TPI basics and other topics, plus instructions for all the tools.
Written by Michael Golden, author of KnitGauge and iKnit NeedleSizer iPhone apps.