416 



wenner: wire resistance standards 



in the first column and the amount in parts per million by which 

 its resistance exceeded its nominal value is given in the succeeding 

 columns. It will be observed that for most of the standards the 

 values on different dates are very nearly the same. As most of 

 these standards belong to the reference set we cannot assume that 

 these figures give anything more than the relative constancy of a 

 number of standards selected because of their small changes as 

 compared with each other. 



With the older or Reichsan start type of standards the relative 

 changes were usually considerably more, especially in standards 

 having resistances of 1000 ohms or above, where the changes in 

 two or three years have sometimes amounted to 0.1 per cent or 

 even more. When, however, the standards of the higher denomi- 

 nation are of the sealed type the changes are much smaller. The 

 values of all the 10,000-ohm standards of the sealed type belong- 

 ing to the Bureau of Standards are given in table II and it will be 



TABLE II 



10,000-Ohm Standards — Sealed Type 



Excess in resistance above nominal value, on different dates at 25° C,, and change in 2 



years in parts per million 



This table shows that during 2^ years only one of the standards changed in resist- 

 ance by as much as 0.005 per cent. 



observed that the resistance of only one of the nine changed in 

 comparison with the reference set by more than 20 parts per mil- 

 lion during two and one-half years. The actual changes as com- 

 pared with the reference set may be somewhat more or somewhat 



