Old topic but... to be sure you have the correct info : The IGV positions are given by the seperate lines as indicated at the top (continious, dashed, dotted and dash-dot) At these IGV positoins, tests are done at several outlet diffuser positions (the numbers at the bottom of these lines in the curves) Example; There are several dashed lines (IGV pos 04) and these have different numbers at the bottom (outlet diffuser vane position). Basically, IGV pivots the curve around the 0 flow max head point and outlet diffusers move the whole curve horizontally.
The numbers are simply the numbers of the actuator arm position (one for the IGV and one for the diffuser), that is on the outside of the machine. You can see them in the left os the picture in the link for the IGV
ASME PTC-10 is the test protocol used at this specific test for warranty on flow/pressure and power consumption.
The curves you see here is a test curve of the machine, a KA44SV where KA44 is the size, S is for outlet diffuser vanes, V for IGV's, from testing (which was done for every machine before it left the factory) in Helsingor, Denmark. The IGV's were used to compensate isentropic head for off-design conditions (determined by pressure measurement, inlet temp measurement and diffuser position), the diffuser vanes for flow control. This way, they got a pretty constant high efficiency over the whole flow range, all the way down to ~45% from the max flow at a constant pressure, at a constant rpm.
You can not really determine flow/pressure from these to find a duty point in practice. These curves are used to program IGV position control in the PLC so when installed, the IGV goes to the optimal position automatically.
There is also another curve that comes with testing, that shows you the efficiency of the machine over the complete working range.
HV-Turbo used to be the world leader in centrifugal compressors for wastewater aeration. They made them from the KA2 (starting at ~ 45 kW) to the KA100 (max. 2.7 MW). They were taken over by Siemens (approx. 2005) and they sold of the whole package to Howden in 2018 I believe. Factory in Helsingor is gone sadly.