Ready References
Stepper Servo Motors
Signal Generators and Their Uses
AAVSO Observing Programs
Numeric Time Scale
Further Reading on Fossils
AAVSO Membership Information
Activity: Estimating Magnitudes
Ready References 
Stepper Servo Motors Signal Generators and Their Uses 
AAVSO Observing Programs Numeric Time Scale Further Reading on Fossils AAVSO Membership Information Activity: Estimating Magnitudes