6. THE SMOOTH SHEET 



205 



graphic portrayal of the survey and it should 

 reflect the care involved in obtaining and 

 compiling engineering data. The standard 

 character of inked lettering is indicated in 

 Fig. 82. Freehand and mechanical pens 

 shall be carefully selected and used to con- 

 form generally with these standards. The 

 experienced draftsman is familiar with the 

 various types of pens available and acquires 

 proficiency with a selected few. A less ex- 

 perienced draftsman should experiment with 

 different types of pens and practice letter- 

 ing until he is able to produce acceptable 

 work. The quality of ink work may be im- 

 proved by tests of pen points and by gently 

 smoothing, rounding, or sharpening the 

 points with fine crocus cloth or oilstone when 

 necessary. A set of pens for various colors 

 is desirable to avoid blending of colors. 



The quality of the ink used is very im- 

 portant. Improper selection of ink can result 

 in faint, non-photographic, or watery detail 

 which becomes more illegible with age. 

 Bottles of coagulated or otherwise aged inks 

 should be discarded. Waterproof drawing 

 inks shall be used and pigmented inks should 

 be stirred or shaken to homogeneous con- 

 sistency before use. Some inks may need to 

 be thickened slightly in order to eliminate 

 the tendency of thin ink to spread into the 

 fibers of the paper. This can usually be ac- 

 complished by natural evaporation on ex- 

 posure to the air. The intensity of the color 

 should be observed and new ink used when 

 colors become weak. Green ink is particu- 

 larly perishable and deteriorates rapidly. 



Special inks shall be used on plastic ma- 

 terials to which ordinary waterproof draw- 

 ing inks will not bind. It may be necessary 

 to use a thinner with such ink, or to thicken 

 it by normal air evaporation. 



6-18 Erasures. — During the construc- 

 tion, plotting, and inking of a smooth sheet 

 every effort should be made to minimize the 

 use of erasers which roughen the paper and 

 cause undesirable spreading and fading of 

 ink work. Unused parts of a smooth sheet 

 should be shielded to prevent unnecessary 

 soiling and subsequent erasing. Soft erasers 

 should be used when erasing becomes neces- 



sary. Ink erasures cannot be made without 

 some damage to the surface, but less dam- 

 age is generally caused by skillful use of an 

 electric eraser than by any other method. 

 Hard abrasive erasers should never be used, 

 even for removal of ink work. With due care 

 and a light touch a smooth inkable surface 

 can be retained. 



6-19 Control stations. — After the pro- 

 jection has been made and verified, the next 

 step is plotting of the control stations. Only 

 those stations used for control shall be 

 plotted. Each station shall be plotted with 

 extreme accuracy, and within 0.15 mm of 

 its true position. The necessary accuracy of 

 critical detail on a hydrographic survey de- 

 pends to a large extend on accuracies in 

 the horizontal control. The actual station 

 point shall be a fine needle hole which 

 is blackened but not enlarged by care- 

 fully rotating a sharp pencil point in the 

 hole. Never use ink for the station dot. 

 Plotting procedures depend on the nature 

 of the control. 



It is important that the plotted stations 

 be carefully and accurately verified before 

 plotting topographic detail and hydrog- 

 raphy. Both the plotter and verifier shall 

 record the actions by initialing in the lower 

 right corner of the smooth sheet, on Stamp 

 No. 42, Hydrographic Survey (Fig. 50). 

 Neither person should proceed until the pro- 

 jection is verified and this action recorded. 

 Should the record be incomplete on receipt 

 of the smooth sheet in the Washington Office, 

 it will then be necessary to verify the plot- 

 ting before proceeding with verification of 

 the hydrography. 



Provision is also made in Stamp No. 42 to 

 record the horizontal datum used in the sur- 

 vey, including the name, date, and geographic 

 position of one of the triangulation stations 

 plotted on the sheet. 



6-20 Triangulation stations. — Triangula- 

 tion stations are always plotted from the 

 computed values of latitude and longitude. 

 The meridional differences (dms.) along 

 adjacent meridians and the parallel differ- 

 ences (dps.) along adjacent parallels are 



