Devices used in understanding and improving production processes. Tool 1: Cause and effect diagram visual representation of the main causes and sub-causes leading to an effect or symptom, also called fishbone diagram (after its shape) or Ishikawa diagram (after its inventor). Tool 2: Check sheet data recording table (matrix) designed by the user to facilitate the recording and interpretation of test results. Tool 3: Control chart visual representation of comparison between actual performance and pre-determined control limits; helps in detecting assignable causes of variation, also called C chart. Tool 4: Flowchart visual representation of relationship between planned performance and actual performance over a period. Tool 5: Histogram graph of side-by-side vertical bars representing a frequency distribution; it reveals patterns that remain hidden in tables of numbers, sometimes it is substituted or supplemented with a Gantt chart. Tool 6: Pareto chart based on Pareto principle (a small percentage of the elements comprising a group accounts for the largest fraction of the value or the impact), it ranks causes from the most significant to the least significant. Tool 7: Scatter chart graph that displays the relationship between two variables; the variable to be predicted (dependent variable) is plotted on the vertical ('Y') axis, and the variable used to make the prediction (independent variable) plotted on the horizontal ('X') axis.