N007 counting clock · 1 cell per second, nonstop (no sleep, no breaks)
Julian year = 31,557,600 s · cells counted per day = 86,400 · per year = 31,557,600

id        | cells (trillion) | years to count | million yr | x Homo sapiens (300k yr) | core
rbc       |             25.0 |        792,202 |       0.79 |                     2.64 | true
hatton_f  |             28.0 |        887,266 |       0.89 |                     2.96 | true
sender    |             30.0 |        950,643 |       0.95 |                     3.17 | true
hatton_m  |             36.0 |      1,140,771 |       1.14 |                     3.80 | true
bianconi  |             37.2 |      1,178,797 |       1.18 |                     3.93 | true
hatton_c  |             17.0 |        538,697 |       0.54 |                     1.80 | false
bacteria  |             38.0 |      1,204,147 |       1.20 |                     4.01 | false
both      |             68.0 |      2,154,790 |       2.15 |                     7.18 | false

Adult spread: 887,266 to 1,178,797 years (0.89–1.18 million): "about a million years"

Comparisons
bacteria_to_human_ratio                       1.267 :1  paper states B/H = 1.3 (±25%)
rbc_share_of_human_cells                       83.3 %  from rounded inputs; the paper states 84% (use 84%)
bacteria_mass_lb                              0.441 lb  0.2 kg (Sender 2016): "under half a pound"
earth_equatorial_circumference_km          40,075.0 km  2 x pi x 6378.137
rbc_lineup_low_km                           168,750 km  diameter 6.75 um
rbc_lineup_low_mi                           104,856 mi  
rbc_lineup_low_laps_of_earth                   4.21 laps  around the equator
rbc_lineup_low_moon_fraction                  0.439 x Moon distance  384,400 km
rbc_lineup_mean_km                          181,750 km  diameter 7.27 um
rbc_lineup_mean_mi                          112,934 mi  
rbc_lineup_mean_laps_of_earth                  4.54 laps  around the equator
rbc_lineup_mean_moon_fraction                 0.473 x Moon distance  384,400 km
rbc_lineup_high_km                          194,750 km  diameter 7.79 um
rbc_lineup_high_mi                          121,012 mi  
rbc_lineup_high_laps_of_earth                  4.86 laps  around the equator
rbc_lineup_high_moon_fraction                 0.507 x Moon distance  384,400 km
sender_counting_8h_per_day_years          2,851,928 yr  optional aside only

Wrote build/cell-count-clock.csv and build/cell-count-compare.csv