You mean the international numbering system? It hasn’t got anything to do with the metric system the former is a positional system in the power of tens and the latter a decimal-based system of measurement, but I can understand that most people outside of South Asia might probably not understand, so here you go.

I’m taking the salary of NASA employees from this page - this is about five years old, so I’m sure the new wages would be slightly higher. GS-15 are the top-level employees at NASA, who earn around $105,123 to $136,659. $136,659 is about ₹11,295,344.66.

From this site, we see that ISRO scientists earn around ₹720,000 to ₹2,400,000). S Somanath, the chairman of ISRO, has disclosed to the local media that he earns about ₹250,000 per months, so on a yearly basis, it would be around ₹3,000,000, which is almost accurate with the salary given in the above site.

Taking the highest range of salary, 11,295,344.66/2,400,000 ~= 4.71 approximately. I’d imagine that low-level employees earn about 8-10 times less than their NASA counterparts. Now, this is not the best way to calculate the difference in wage, perhaps I should’ve taken the mean and gone about with it, but it should still give you a rough idea about how misleading the “25 times less income” claim is.