How does a Geiger counter, such as RD1706, converts counts per minute to micro Sievert per hour? The RADEX RD1706 contains two SBM20-1 type Geiger–Müller counters.
I understand how the counts per minute value can be computed. But how is the micro Sievert per hour value obtained? And what is its meaning?
 A: The sievert (Sv) is a derived unit of ionizing radiation dose in the international system of units. It is a measure of the health effect of low levels of radiation on the body. For radiation dose assessment, it shows the probability of cancer and DNA damage. One sievert carries with it a 5.5% chance of developing cancer. One sievert = 100 rem. Two commonly used prefixes are the millisievert and the microsievert (1 μSv = 0.000001 Sv). Frequently used units for dose rate indications on instruments are μSv/h (microsieverts per hour).
The definition of the sievert given by the International Committee for Weights and Measures is $H = Q \times D$, where $H$ is the quantity dose equivalent, $D$ is the absorbed dose of ionizing radiation and $Q$ is the dimensionless quality factor defined as a function of linear energy transfer. The unit for the sievert is joule per kilogram according to the ICRP.
For the counter itself, it is calibrated to the proper value using radiation metrology techniques which trace the values to a national standard and then relate them to an operational quantity. Another method of calibrating can be done via the radiation type weighting factor described here.
Hope this helps!
Note:
Considering your comment asking how to convert sieverts per minute to microsieverts per hour, I created an example calculation.
If your value is 1 sievert/minute (which is a really high value; I'm just using this number for roundness):
$$1 \frac {Sv}{min} * \frac {60 min}{1 hour} * \frac {10^6 \mu Sv}{1 Sv} = \frac {1*60*10^6}{1*1*1} \frac {Sv * min * \mu Sv}{min * hour * Sv} = 60,000,000 \frac {\mu Sv}{hour}$$
Note 2:
In the case of your updated question in the comments, technically there isn't really a direct equation converting counts per minute (CPM) to microsieverts because CPM is an electron count and microsieverts is a count of bodily damage.
A: The conversion between CPM and uSv/h is done via a conversion factor. According to this site:

Conversion factor is usually calibrated to gamma activity from
  a Co-60 or Cs-137 source.  It is specific to your tube, the
  radioisotope, and type of radiation.  It is usually given only for
  gamma radiation.  (actual gamma sensitivity is something like 1-10%
  depending on the isotope)

For a given tube, there is no consensus on which value to use. You can find here a list of different values used by different people.
