updated efficiency column to mirror std metric of MFLOPS/W

README.md

 # pi calculation benchmark
 [http://fab.cba.mit.edu/classes/MAS.864/text/benchmark.pdf](http://fab.cba.mit.edu/classes/864.17/text/benchmark.pdf)
 
-|estimated GFlops|estimated GFlops/W|code|description|system|date|
+|estimated GFlops|estimated MFlops/W|code|description|system|date|
 |---|---|---|---|---|---|
 |88,333|-|[mpimppi.c](hybrid/mpimppi.c)|C, MPI+OpenMP, 1024 nodes, 64 cores/node, 4 threads/core<br>cc mpimppi.c -o mpimppi -O3 -ffast-math -fopenmp|Argonne ALCF Theta<br>Cray XC40|Oct 9, 2019|
 |272|-|[threadpi.c](C/threadpi.c)|C, 96 threads<br>gcc threadpi.c -o threadpi -O3 -ffast-math -pthread|Intel 2x Xeon Platinum 8175M|Jun 3, 2019|
@@ -22,5 +22,5 @@
 |0.57|-|[pi.c](C/pi.c)|C<br>gcc pi.c -o pi -lm|Intel i7-8700T|Nov 17, 2018|
 |0.47|-|[numpi.py](Python/numpi.py)|Python, NumPy|Intel i7-8700T|Nov 17, 2018|
 |0.029|-|[pi.py](Python/pi.py)|Python|Intel i7-8700T|Nov 17, 2018|
-|0.0168|0.233<br>calculated|[pi.c](https://gitlab.cba.mit.edu/zfredin/samd51_benchmarks)|C<br>floats, -O3, gcc-arm-none-eabi, 160 MHz|SAMD51J20A<br>ARM Cortex M4F|Oct 18, 2019|
-|0.0128|0.171<br>calculated|[pi.c](https://gitlab.cba.mit.edu/zfredin/stm32f412_core/tree/master/nucleo-f412zg/pi)|C<br>floats, -O3, gcc-arm-none-eabi, 84 MHz|STM32F412<br>ARM Cortex M4F|Oct 8, 2019|
+|0.0168|233<br>calculated|[pi.c](https://gitlab.cba.mit.edu/zfredin/samd51_benchmarks)|C<br>floats, -O3, gcc-arm-none-eabi, 160 MHz|SAMD51J20A<br>ARM Cortex M4F|Oct 18, 2019|
+|0.0128|171<br>calculated|[pi.c](https://gitlab.cba.mit.edu/zfredin/stm32f412_core/tree/master/nucleo-f412zg/pi)|C<br>floats, -O3, gcc-arm-none-eabi, 84 MHz|STM32F412<br>ARM Cortex M4F|Oct 8, 2019|