(Another class of physical distance indicator is the standard ruler.

A standard ruler is an astronomical object whose approximate size is known.

Some work has been done attempting to use radio galaxies as standard rulers to determine cosmological parameters.

Rather, D provides a standard ruler.

This is commonly used to observe so called standard rulers, for example in the context of baryon acoustic oscillations.

In 2008, galaxy diameters have been proposed as a possible standard ruler for cosmological parameter determination.)

Furthermore, the redshift interval, , extended by the standard ruler is directly related to the Hubble constant:

The BAO signal is a standard ruler such that the length of the sound horizon can be measured as a function of cosmic time.

The angle subtended by a standard ruler as a function of redshift is related to the Hubble parameter, through the concept of the angular diameter distance.

The length of this standard ruler ( 490 million light years in today's universe) can be measured by looking at the large scale structure of matter using astronomical surveys.

The length scale at which this signal occurs throughout the universe can be used as a Standard ruler to constrain cosmology, and in particular, the evolution of dark energy.

This signal in the power spectrum can be used as a standard ruler to map out the evolution of the Hubble parameter, , and the angular diameter distance with redshift.

In the same way that supernova experiments provide a "standard candle" for astronomical observations, BAO matter clustering provides a "standard ruler" for length scale in cosmology.

With Daniel Eisenstein and Wayne Hu, he introduced the idea of using Baryon Acoustic Oscillations as a Standard Ruler.

As the equation above shows, by measuring the angle subtended by the standard ruler as a function of redshift, we are effectively measuring the integral of over redshift.

In principle, the expansion of the universe can be measured by taking a standard ruler and measuring the distance between two cosmologically distant points, waiting a certain time, and then measuring the distance again.

For the case of BAO, the physical size, , of the standard ruler (i.e. the sound horizon at recombination) can be constrained from the CMB-based measurements of and .

The primary goal of this study is to use an intrinsic feature in the distribution of galaxies as a "standard ruler" to relate distance to redshift and improve our knowledge of the nature of dark energy.

In practice, standard rulers are not straightforward to find on cosmological scales and the time-scales for waiting to see a measurable expansion of the universe today are too long to be observable by even generations of humans.

A pattern made to match an existing part would be made as follows: First, the existing part would be measured using a standard ruler, then when constructing the pattern, the pattern maker would use a contraction rule, ensuring that the casting would contract to the correct size.