226 EMPLOYMENT PSYCHOLOGY 6. Q. Why chamber? A. If the chamber is too large the shell will swell and cannot be extracted in the regular way. 7. Q. Why firing pin? A. If the firing pin is too long there will be the danger of premature fire, if too short, of misfire. 8. Q. Why barrel? A. If there is a seam in the barrel when shot it will burst open and if the barrel is not straight the gun will not shoot straight. 9. Q. Why sight alignment? A. The alignment of sight is essential to correct shooting. 10. Q. What experience as an assembler other than on guns? A. Have had several years’ experience on sewing machines, typewriters, etc. 11. Q. What kind of work requiring particularly close filing have you done? A. Small-tool work. These are valuable questions because they require specific answers about concrete and specific elements in the work of gun assembling. However, definite as they are, they could not be used as they stand with any certainty as to their value. It is first of all necessary to experiment with these questions on a sufficient number of men actually engaged in this work, in order to find out whether the questions are such that the best workers obtain the highest grade in the test and the poorest workers the lowest grade. In other words, it is necessary to find the correla tion between the performance of the men in the test and their actual ability at their trade. Moreover, it is also necessary, by the process of trial and error described in previous chapters, to eliminate ambiguous words, catch questions, “guess” answers, and questions which permit a lengthy or indefinite explanation. In short, trade tests, whether in the form of questions or any other form, must