At someone's request,I have made measurements of 3 indicators. A last Word in new condition,A Mitutoyo in new condition,and a plunger back Starrett in new condition. The Starretts were kept in boxes,and the Mitutoyo was out in the open,attached to a magnetic base,where it had the possibility of collecting shop dust from the air. It seemed clean.
The way I tested them was by pressing each stylus on a very delicate digital stone weighing scale that registers in 1/10 grams. Each indicator was pressed until the dial read .005".
The Last Word took 2.2 grams to reach .005". The Mitutoyo took 1.0 grams. The Starrett plunger back took 4.4 grams. Each were oiled with Starrett Instrument oil,but only on the joints where their stylii swivel. I do not let oil get inside them.
So,the Last Word took more than twice the force of the Mitutoyo to register .005". The Starrett plunger back,freshly oiled,too,took more than twice the force of the Mitutoyo to register .005". The plunger back is an entirely different type of indicator mechanism,and I think it is not really fair to compare it to the others. I did it because I had it handy,and out of curiosity,included it.
This was a scientific test and cannot be called an opinion because actual data was collected,all indicators were in new condition,and all were oiled with Starrett instrument oil.WD 40 has never been used on my indicators because I know it is bad,and leaves a varnish deposit.
Previously,for several years,I used a cheaper Chinese indicator,which to my trained fingers,felt about as sensitive as the Mitutoyo. I got the Mitutoyo cheap,hardly used,and gave my Chinese one to my journeyman. I never tested it because we did not have the stone scale,and the subject never came up.