Comparative Scales

• Comparative Scale consists of two scales of the same RF, but graduated to read different unit,constructed separately or one above the other.
• Used to compare distances expressed in different systems of unit e.g. kilometers and miles,
• centimeters and inches.The two scales may be plain scales or diagonal scales or Vernier scales.  

1 Mile = 8 fur. = 1760 yd = 5280 ft

Construct a plain comparative Scales of RF = 1/624000 to read up to 50 kms and 40 miles.
On these show the kilometer equivalent to 18 miles

Draw a 4 in. line AC and construct a plain scale to represent mile and 8cm line AB and construct the kilometer scale below the mile scale.
On the mile scale, determine the distance equal to 18 miles (PQ)
Mark P’Q’ = PQ on the kilometer scale such that P’ will coincide with the appropriate main division.  Find the length represented by P’Q’. 
P’Q’ = 29 km.           (1Mile = 1.60934 km)