This standard applies to pressure resistant circular sight glasses of soda-lime-glass without limitation in the range of low temperature, which can be subjected to one-sided liquid or gas pressure at temperatures up to 150 ° C and without limitation of the temperature below the ambient temperature. At temperatures between 100 ° C and 150 ° C, the scope of this standard is limited by chemical erosion of sight glass plates in contact with alkaline solutions. The conditions for use up to the pressure and temperature limits mentioned in the document are considered.