How did Jocelyn Bell Burnell discover the periodicity of CP 1919? According to Wikipedia,
in 1967, a radio signal was detected using the Interplanetary Scintillation Array of the Mullard Radio Astronomy Observatory in Cambridge, UK, by Jocelyn Bell Burnell. The signal had a 1.337302088331-second period and 0.04-second pulsewidth.[4] It originated at celestial coordinates  19h 19m right ascension, +21° declination. It was detected by individual observation of miles of graphical data traces. Due to its almost perfect regularity, it was at first assumed to be spurious noise, but this hypothesis was promptly discarded. The discoverers jokingly named it little green men 1 (LGM-1).
Also from Wikipedia,

My question is the signal was just measured from the chart directly?
Yes - at that time, the chart was the source of data used for analysis. Jocelyn visually reviewed hundreds of metres of traces every night looking for quasars (the reason the Interplanetary Scintillation Array was built)
The wiggle looked different from expected signals, and in fact was misidentified as interference at first, but when she noticed it again, and again, she conducted further analysis, identifying its repetition rate of 1.337 seconds.
From the New Yorker:

Bell Burnell - who analyzed the roughly seven hundred feet of paper generated each week as galactic radio waves were recorded in inked peaks - noticed a faint signal arriving from one slice of sky. Then it disappeared. In November, she saw it again. By adjusting the speed of the recording device, she determined that the signal came in every 1.34 seconds, a regular beat against the background static of the cosmos.

All from visual measurement of the trace!