f. Thread a screw through the 2.0 mm hole (f). This screw is 

 used for adjusting the gap between the relay plate and the 

 coil. The proper gap is critical to the 'firing' of the relay. 



(1) Adjust the gap on the 12 V relay to 0.559 mm, using a 

 feeler gauge. 



(2) Adjust the gap on the 6 V relay to 0.254 mm. 



g. Attach felt tip pens to the pen arm (g). 



Constructing the Plexiglass Stage and 

 Attaching the Pen Arm Relays 



Materials 



(1) 3.0 mm thick plexiglass stock 22 x 15 cm (for sides and- the 

 relay plate) 



(1) 6.0 mm thick plexiglass stock 8 x 15 cm (for the base and top 

 of the stage) 



(2) brass bolts 



(1) 25 ml bottle of ethylene dichloride 



(2) brass screws 



Instructions (Refer to Figs. 9-11) 



1. Refer to Fig. 10 for dimensions of plexiglass sections and 

 location of drill holes and grooves. 



a. Cut each section. 



b. Drill all required holes. 



c. Saw a groove in each side piece for attachment of the LWI 

 relay plate 



2. Place the plexiglass base plate lengthwise 6.0 cm from cen- 

 ter of the guidepost and 3.3 cm from the back edge of the 

 hygrothermograph base plate (Fig. 9). 



a. Use a scribe to etch the position of the plexiglass base 

 plate. 



b. Keep the plexiglass base plate in place, and use as a 

 template to mark the position of the holes to be drilled in 

 the base of the hygrothermograph (Fig. 9). 



(1) Drill the two outer holes with a 4.0 mm drill bit, and use 

 a tap corresponding to the drill bit size to thread the 

 holes. 



(2) Drill the center hole with a 6.0 mm bit. 



3. Attach the 12 V and 6 V relays to the stage (Fig. 11). 



a. Drill two 4.0 mm holes in stage for attaching the relays 

 (Fig. 10). Screw the 12 V relay to the top section of the 

 stage. Screw the 6 V relay to the LWI relay plate. 



