Definition:Elementary Charge/Historical Note

Historical Note on Elementary Charge
Until the $2019$ definition of the elementary charge as exactly $\E = 1.60217 \, 6634 \times 10^{−19} \, \mathrm C$, it was the subject of measurement.

This measurement has been accomplished to greater and greater accuracy over time.

By $1964$, it was established as:
 * $\E = 1 \cdotp 60219 \, 17 \pm 0 \cdotp 00000 \, 70 \times 10^{−19} \, \mathrm C$