Sadly, a 20% fixed "service surcharge" is becoming the norm in SF and I'm talking fine dining establishments (Michelin 3*).
The small print says something to the effect of "if you disagree let us know and we will remove it".
AFAIK the 20% is calculated on the entire bill inclusive of CA taxes and 4% SF mandate.

I personally find it an abominable practice.
First of all, I don't give diddly squat of how the restaurant owner apportions his/her receipts. When I go to my dentist he doesn't itemize the bill "for my dental assistant, for utilities bill, etc."
It would be much more honest if they simply jacked up prices, which are already high and oftentimes come has a single charge "$325 Chef's tasting menu". Dear Chef, just charge $400 and save me the implied stories about the orphans and health care for all.
I guess the majority of the SF well-to-do crowd feels a little less hypocritical when they can think that they just dropped half a grand on a meal, but some of it went to the waiting staff and to the State.

Secondly, portable card readers are ok, but they put some pressure in selecting the correct tip on the fly, with the waiter there looking. From that point of view I really prefer the old paper receipt where I can take my time and enjoy a little more privacy.