Time and Frequency from A to Z:  T to Te

A temperature-compensated crystal oscillator.  A TCXO is a type of quartz oscillator that compensates for temperature changes to improve stability.  In a TCXO, the signal from a temperature sensor is used to generate a correction voltage that is applied to a voltage-variable reactance, or varactor. The varactor then produces a frequency change equal and opposite to the frequency change produced by temperature. This technique does not work as well as the oven control used by an OCXO, but is less expensive. Therefore, TCXOs are used when high stability over a wide temperature range is not required.

One trillion cycles per second (10¹² Hz).

An astromonical time scale which equals TAI + 32.184 s. The uncertainty of TT is +/- 10 microseconds.  It replaced the now obsolete Ephemeris Time scale in 1984.

A measurement or calibration compares a device under test (DUT) to a standard or reference. The standard should outperform the DUT by a specified ratio, called the Test Uncertainty Ratio (TUR).  Ideally, the TUR should be 10:1 or higher. The higher the ratio, the less averaging is required to get valid measurement results.