The Quartzlock A1000 Frequency Reference is a 1U rack-mounted Rubidium Atomic Clock based instrument. Exceptionally low drift is a unique parameter for the A1000. The hourly and daily stability and drift performance are "best available", typically 8x10-13/day, at the 10MHz, low distortion, sine wave, 50 Ohm output. Very high reliability stems from the physics package and Quartzlock's electronics. Long term production has led to MTBF's of well over 100,000 hours. The A1000 Frequency Reference has a high reliability inbuilt 110 - 240V ac power supply with low noise characteristics.