[en] Since 1996, the IAEA maintains standards for Low Dose Rate (LDR) brachytherapy dosimetry. The sources have been calibrated at the National Institute for Standards and Technology (NIST), USA. Thus, the well type chamber calibrations provided by the IAEA yield traceability to NIST. For the maintenance of the standards, a well type chamber (HDR 1000 Plus, Standard Imaging, USA) and a dedicated electrometer (CDX-2000A, Standard Imaging, USA) are used. The constancy of the output from the standards is checked frequently and always prior to a well type chamber calibration. The calibration factors are valid at the ambient conditions of 20 deg. C and 101.3 kPa. For air cavity chambers, the International Commission on Radiation Units and Measurements (ICRU) recommends that the measured charge or current be corrected for the presence of water vapour in the air. The recommended correction factor is 0.997 for measurements in an external ⁶⁰Co beam and at ambient RH between 20% RH and 70% RH. A similar recommendation does not exist for well type chamber dosimetry, and consequently, no correction is applied for the presence of water vapour in air. It is important that the periodic variation of the output be solved. In order to find out its cause, the SSDLs possessing a well type chamber are asked to perform similar frequent constancy checks and report the results to the IAEA. The following should be stated in the report: 1. Measured currents (or charge) corrected for temperature and pressure and source decay with a statement of the used half-life. 2. Dates of measurement. It is recommended that the measurements be done frequently, preferably on a weekly basis, or at least twice a month, for a period of approximately 6 months. 3. Type of source used in the constancy checks (e.g. ¹³⁷Cs, ²⁴¹Am) including its strength (e.g. in terms of reference air kerma rate, air kerma strength, apparent activity or any other quantity). 4. Electrometer model. 5. Type of well type chamber. Note that the request is not limited to identical well type chambers as that at the IAEA Dosimetry Laboratory, nor is it limited to chambers that are open to ambient conditions. Thus, also sealed chambers can be used in the measurements. A summary of the results will be presented in a forthcoming issue of the SSDL Newsletter. The contributors will be acknowledged