The angle protractor scale reads the rotational angle of the shifter or derailleur mount against a reference point, while the sliding ruler, which spans a 0-20cm arm with a 0-100 pointer scale, measures linear position along the frame or mount. Using both together lets you record a precise reference setup once, then reproduce that exact position if you ever remove and refit the part.

Even a small deviation in mounting angle can change cable pull geometry and lead to hesitant, sluggish or inconsistent shifts, especially on precise modern drivetrains with narrow gear spacing. Getting the position exactly right the first time reduces the amount of fine-tuning needed afterward at the barrel adjuster.

This is a more specialised, precision-oriented tool typically used by shops and serious home mechanics who want shop-level accuracy in their own setup work, particularly if you frequently swap components or maintain multiple bikes. If you only occasionally adjust your own shifting, a basic setup by feel followed by index adjustment is usually sufficient, but this tool removes the guesswork for anyone who wants repeatable precision.

Yes, if your shifting has become inconsistent over time, checking the current angle and position against your original reference measurement with this tool can reveal whether the component has slipped or shifted from its correct setup. This makes it useful for troubleshooting, not just for fresh installs.

The tool's scales and sliding arm are built to hold their calibration accurately over repeated use, which is important since even small measurement drift would defeat the purpose of a precision positioning tool. With careful storage and handling, it is designed to remain a reliable reference tool for years of setup work.

Yes, this is a genuine Le Bicycle precision tool sold through DoGoodCo, manufactured to keep its angle and ruler scales accurate over time. If your tool arrives damaged or the scales read inconsistently, our support team will help arrange a replacement as per store policy.