Subject: Re: Buffett interview 2019. BRK vs SPY
Profits can rise faster than sales if RoS keeps rising.
Intuitively, more modern firms have a higher net margin than the older firms.
Historically, also true. I took data from multpl.com P/E (by month) and P/S (by quarter); and massaged it align dates (add a day to P/S date to get the corresponding P/E date).
Although it is quite bumpy, RoS does seem to be rising steadily for the last 22 years:

Date P/S P/E RoS
07/01/2023 2.54 25.8 9.85%
04/01/2023 2.34 23.9 9.81%
01/01/2023 2.19 22.9 9.55%
10/01/2022 2.09 20.4 10.20%
07/01/2022 2.28 20.5 11.10%
04/01/2022 2.8 22.4 12.50%
01/01/2022 3.04 23.1 13.20%
10/01/2021 2.85 24.4 11.70%
07/01/2021 2.94 26.6 11.10%
04/01/2021 2.85 29.9 9.53%
01/01/2021 2.76 36 7.68%
10/01/2020 2.47 35.3 7.00%
07/01/2020 2.26 32.4 6.97%
04/01/2020 1.83 25 7.33%
01/01/2020 2.28 24.9 9.16%
10/01/2019 2.14 22 9.71%
07/01/2019 2.13 22.3 9.56%
04/01/2019 2.08 21.6 9.65%
01/01/2019 1.87 19.6 9.54%
10/01/2018 2.2 21.2 10.40%
07/01/2018 2.1 22.3 9.40%
04/01/2018 2.1 22.5 9.32%
01/01/2018 2.17 25 8.69%
10/01/2017 2.09 23.7 8.83%
07/01/2017 2.04 23.4 8.73%
04/01/2017 2.02 23.2 8.69%
01/01/2017 1.95 23.6 8.27%
10/01/2016 1.9 23.6 8.06%
07/01/2016 1.86 24.5 7.59%
04/01/2016 1.83 24 7.63%
01/01/2016 1.81 22.2 8.16%
10/01/2015 1.69 22.7 7.45%
07/01/2015 1.8 22.4 8.04%
04/01/2015 1.79 21.4 8.36%
01/01/2015 1.77 20 8.84%
10/01/2014 1.71 18.5 9.24%
07/01/2014 1.72 19 9.07%
04/01/2014 1.66 18.4 9.05%
01/01/2014 1.66 18.1 9.15%
10/01/2013 1.51 17.9 8.45%
07/01/2013 1.45 18.1 8.00%
04/01/2013 1.43 17.7 8.08%
01/01/2013 1.31 17 7.69%
10/01/2012 1.34 16.6 8.06%
07/01/2012 1.27 15.6 8.17%
04/01/2012 1.32 15.7 8.41%
01/01/2012 1.19 14.9 8.00%
10/01/2011 1.1 13.9 7.93%
07/01/2011 1.31 15.6 8.39%
04/01/2011 1.35 16.2 8.33%
01/01/2011 1.31 16.3 8.04%
10/01/2010 1.21 15.9 7.61%
07/01/2010 1.11 15.7 7.06%
04/01/2010 1.27 19 6.68%
01/01/2010 1.23 20.7 5.94%
10/01/2009 1.17 42.1 2.78%
07/01/2009 0.97 102 0.95%
04/01/2009 0.8 120 0.67%
01/01/2009 0.87 70.9 1.23%
10/01/2008 1.08 27.2 3.97%
07/01/2008 1.19 25.4 4.69%
04/01/2008 1.26 23.9 5.28%
01/01/2008 1.43 21.5 6.66%
10/01/2007 1.52 20.7 7.35%
07/01/2007 1.52 18.4 8.28%
04/01/2007 1.47 17.5 8.41%
01/01/2007 1.49 17.4 8.58%
10/01/2006 1.43 17.1 8.34%
07/01/2006 1.38 16.6 8.31%
04/01/2006 1.44 17.8 8.10%
01/01/2006 1.43 18.1 7.91%
10/01/2005 1.44 17.6 8.16%
07/01/2005 1.44 19 7.58%
04/01/2005 1.46 19 7.68%
01/01/2005 1.54 20 7.70%
10/01/2004 1.47 19.2 7.64%
07/01/2004 1.54 19.5 7.89%
04/01/2004 1.55 21.2 7.30%
01/01/2004 1.56 22.7 6.86%
10/01/2003 1.43 24.8 5.78%
07/01/2003 1.42 27.6 5.14%
04/01/2003 1.25 28.1 4.46%
01/01/2003 1.3 31.4 4.14%
10/01/2002 1.17 29.2 4.00%
07/01/2002 1.39 32.5 4.28%
04/01/2002 1.6 43.8 3.65%
01/01/2002 1.56 46.2 3.38%
10/01/2001 1.41 39.7 3.55%
07/01/2001 1.64 35.5 4.62%
04/01/2001 1.54 28 5.51%
01/01/2001 1.77 27.6 6.42%