Keeping things "aligned and straight" while building is crucial for a well built plane.
As we construct the assemblies that make up our homebuilt aircraft (wings, fuselage, etc) the pressure is always on to keep the parts aligned, straight, or level with their adjacent components. This includes insuring that long parts like wing skeletons have no "twist" induced into their length before final riveting. A long structure like a fuselage is also subject to picking up a twist as we observe from front to rear.
An inexpensive, high tech tool that allows us to measure and monitor such subtle variances in our work is the battery powered laser. Like stretching a string from one end of our work to the other, the light beam from the portable laser allows us to easily see the deviations in our work as we try to keep everything "straight". This short video provides some introductory information for aircraft builders that are new to using the laser tool for their aircraft construction.