Calc 1's last write | Calc 2's last write | What both calcs read
0                   | 0                   | 3
1                   | 0                   | 0
2                   | 0                   | 1, then 0 after two seconds
3                   | 0                   | 0
0                   | 1                   | 0
0                   | 2                   | 0
0                   | 3                   | 0
1                   | 1                   | 2
1                   | 2                   | 0
2                   | 1                   | 0
2                   | 2                   | 1