These are the packages that would be merged, in order:

Calculating dependencies ... done!
Dependency resolution took 1.22 s (backtrack: 0/20).

[ebuild  N     ] dev-cpp/nlohmann_json-3.12.0-r1::gentoo  USE="-test" 9452 KiB
[ebuild  N     ] dev-libs/libev-4.33::gentoo  USE="-static-libs" 557 KiB
[ebuild  N     ] sci-libs/fftw-3.3.10-r1:3.0/3::gentoo  USE="openmp threads -doc -fortran -mpi -test (-zbus)" CPU_FLAGS_X86="avx avx2 fma3 sse sse2 -fma4" 4047 KiB
[ebuild  N     ] sci-libs/libnova-0.16.0:0/0.16::gentoo  USE="-doc -examples" 888 KiB
[ebuild  N     ] dev-lang/cfortran-20210827-r1::gentoo  USE="-examples -test" 101 KiB
[ebuild  N     ] virtual/fortran-0-r1::gentoo  USE="openmp" 0 KiB
[ebuild  N     ] dev-cpp/cpp-httplib-0.60.1:0/0.60::gentoo  USE="ssl zlib -brotli -mbedtls -test -zstd" 1961 KiB
[ebuild  N     ] sci-libs/cfitsio-4.7.0:0/10-r1::gentoo  USE="bzip2 -curl -test -tools" 2113 KiB
[ebuild  N     ] sci-libs/gsl-2.7.1-r3:0/27::gentoo  USE="deprecated -cblas-external -static-libs" 7346 KiB
[ebuild  N     ] dev-libs/libusb-1.0.30:1::gentoo  USE="-debug -doc -examples -static-libs -test -udev -verify-sig" 641 KiB
[ebuild  N     ] virtual/libusb-1-r2:1::gentoo  USE="-udev" 0 KiB
[ebuild  N     ] dev-libs/hidapi-0.15.0::gentoo  USE="-doc" 356 KiB
[ebuild  N     ] sci-libs/indilib-2.2.4.2:0/1::gentoo  USE="-ogg -rtlsdr -test" 3774 KiB

Total: 13 packages (13 new), Size of downloads: 31231 KiB