code: private function registerNewCalc($from, $to)
      {
          $result = null;
          $ctx = new \Praxigento\Core\Data();
          $ctx->set($this->servPeriodAdd::CTX_IN_DSTAMP_BEGIN, $from);
          $ctx->set($this->servPeriodAdd::CTX_IN_DSTAMP_END, $to);
          $ctx->set($this->servPeriodAdd::CTX_IN_CALC_TYPE_CODE, Cfg::CODE_TYPE_CALC_FORECAST_PLAIN);
          $this->servPeriodAdd->exec($ctx);
          $success = $ctx->get($this->servPeriodAdd::CTX_OUT_SUCCESS);
          if ($success) {
              $result = $ctx->get($this->servPeriodAdd::CTX_OUT_CALC_ID);
          }
          return $result;
      }
docs: Register new period and related calculation.
  
  @param string $from begin of the period (YYYYMMDD)
  @param string $to end of the period (YYYYMMDD)
  @return int registered calculation ID