Use the noun touchstone to describe a basis for comparison. For example, a filmmaker's touchstone might be her all-time favorite movie; she wants her movie to be that good or similar to it in some way.

Touchstone as it is defined today comes from an actual stone. In the late 15th century, gold and silver was rubbed, or touched against black quartz — the touchstone — to determine the purity of the metals. This was done by looking at the color of the streaks left on the stone. This is why a touchstone, in the figurative sense as it is used today, is a measuring tool.

Definitions of touchstone
  1. noun
    a basis for comparison; a reference point against which other things can be evaluated
    synonyms: criterion, measure, standard
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    a standard by which something can be measured or judged
    ERA, earned run average
    (baseball) a measure of a pitcher's effectiveness; calculated as the average number of earned runs allowed by the pitcher for every nine innings pitched
    GPA, grade point average
    a measure of a student's academic achievement at a college or university; calculated by dividing the total number of grade points received by the total number attempted
    procrustean bed, procrustean rule, procrustean standard
    a standard that is enforced uniformly without regard to individuality
    a measure or standard used for comparison
    medium of exchange, monetary system
    anything that is generally accepted as a standard of value and a measure of wealth in a particular country or region
    graduated table, ordered series, scale, scale of measurement
    an ordered reference standard
    gauge, standard of measurement
    accepted or approved instance or example of a quantity or quality against which others are judged or measured or compared
    an imaginary line or standard by which things are measured or compared
    a standard or model or pattern regarded as typical
    legal tender, stamp, tender
    something that can be used as an official medium of payment
    the most common medium of exchange; functions as legal tender
    the metal or paper medium of exchange that is presently used
    Beaufort scale, wind scale
    an international scale of wind force from 0 (calm air) to 12 (hurricane)
    a numerical scale used to compare variables with one another or with some reference number
    logarithmic scale
    scale on which actual distances from the origin are proportional to the logarithms of the corresponding scale numbers
    Mercalli scale
    a scale formerly used to describe the magnitude of an earthquake; an earthquake detected only by seismographs is a I and an earthquake that destroys all buildings is a XII
    Mohs scale
    a scale of hardness of solids; talc is 0 and diamond is 10; ordering is determined by which substance can scratch another substance
    Richter scale
    a logarithmic scale of 1 to 10 formerly used to express the magnitude of an earthquake on the basis of the size of seismograph oscillations
    moment magnitude scale
    a logarithmic scale of 1 to 10 (a successor to the Richter scale) that enables seismologists to compare the energy released by different earthquakes on the basis of the area of the geological fault that ruptured in the quake
    temperature scale
    a system of measuring temperature
    wage scale, wage schedule
    a schedule of wages paid for different jobs
    type of:
    metric, system of measurement
    a system of related measures that facilitates the quantification of some particular characteristic
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