Recurve and Compound Options
Beiter Limb gauges these can be fitted to the limbs to find the centre of the limb.
They can aid straightening up the limbs and limb tips with the string.
They should not be used to adjust the limb alignment to get the string running directly through the limb guages and the centre of the limb bolts on the handle, this can lead to what many consider is a straight bow but sometimes the limb tips can be out of line and don't track back in a straight line.See article here Limb Alignment
For compound bows they offer a great datum points for the strings and cables