The values shown are the total amount of U-235, irrespective of enrichment levels. The uranium shipped in 1944, for example, had an average enrichment level no higher than 70.6% (per page 4 in the same document this chart came from). By July 1945, this average had been raised to 81.6%, and by December 29, 1946, the average enrichment level of the 1,041,026.5 grams of uranium shipped was "Approx. 95%"

To get the total amount of uranium in grams, the value for any point on the graph must be multiplied by the enrichment level. So, for example, the table accompanying indicates that on 7/17/1945, 52,506.91 grams of U-235 had been shipped, with an average enrichment of 81.6% U-235. So the total amount shipped by that point, by mass, was around 64,347 grams.

The rate of production varied from around 56 grams of uranium per day in late 1944, up to nearly 1 kg per day in October 1945. For the year of 1946, the average rate of production was 2,341.43 grams per day.

The graph indicates several milestones:

• First Beta Product Shipment (June 1944): The Y-12 facility consisted of an Alpha and Beta tracks in separate building. Alpha began operation in late 1943/early 1944. Beta began operation in March 1944. The Alpha process would enrich the uranium to about 10% U-235.
• K-25 Feed to Alpha (March 1945): K-25 was the gaseous diffusion uranium enrichment facility at Oak Ridge. Originally, K-25 and Y-12 were considered independent methods to enrich uranium. However in early 1945, it was realized that the inefficiencies of K-25 (at that time) were such that it would be better to use it to pre-enrich uranium that was then sent to Y-12. This indicates when the K-25 feed was added to the Alpha process, when it was initially only very minimally enriched.
• K-25 Feed to Beta (June 1945): Indicates when the K-25 feed was added to the Beta process, at which point it was already enriched to 20-25%, decreasing the amount of separative work that Y-12 had to do dramatically.
• Hiroshima (August 1945): The Little Boy bomb's final pieces were sent to Tinian at the end of July 1945, and consisted of 64 kilograms of (on average) 80% enriched uranium. The weapon was dropped on Hiroshima on 6 August 1945. At the time it was dropped, as the graph indicates, it contained essentially all of the US enriched uranium supply. If another Little Boy bomb was to be made, the graph implies that sufficient fuel would have been available by October 1945.

The overall appendix has the date "10/7/47" written on its cover, though it may have been written earlier than this (it contains data through December 31, 1946).