Hello Sumedh.
Thank you for your answer. I was using FusionCharts v. 3.2.2. Yeasterday I got the version 3.3.1 and I was trying once again to add trendlines:
<trendLines> <line startValue="80" color="FF0000" parentYAxis="S"></line> </trendLines>
but the effect was actually worse. When I was using v.3.2.2, the trend line gets the value from the PRIMARY y axis, but the labels was on the SECONDARY y axis. Now I have got label also on the PRIMARY y axis. I do not know yet, what I am doing wrong..
Please help me if you can.