Oh, it's no use taking it for granted. It is not good to mislead others.

14H(+)+6s2o 3(2-)+cr2o 7(2-)= 3s4o 6(2-)+2Cr(3+)+7H2O

There is a superscript in brackets.

Potassium dichromate: sodium thiosulfate = 1: 6, which is 1: 1 if calculated by (1/6)K2Cr2O7.

There are preparation and calibration methods in GB/T60 1.