A simple machine for analyzing chromosome replication by DNA combing. (A) The assembled combing machine. (B) Installation of coverslip holder and sample reservoirs on M3 support posts. (C) Motor shield circuit diagram. A, Arduino Uno analog pins; D, Arduino Uno digital pins; C, capacitor; EN, enable pin; IC, integrated circuit (L293D); IN, input pin; kΩ, kilohm; M, motor; OUT, output pin; R, resistor; S1, motor power level switch; S2, lower travel-limit switch; S3, upper travel-limit switch; S4, push button; V, volt; Vmotor, voltage input for motor; +V, voltage supply for the integrated circuit; μF, microfarad.