How did the median first crosscut change over the years?

For each year, I have calculated the median for the move number on which the first crosscut occurred, over all games for that year. Before 1800, the sample sizes are too small to produce meaningful data. Also, there are some spikes around 1875 and the 1940s; this may be because there are few games for those years.

Click and drag on the small bottom chart to pan and zoom the main chart.