For my ponds I used google earth. You can move cursor over map and elevation will show in lower right hand corner. In my case elevations were fairly accurate relative to each other. I like it because it allows you to see the physical attributes along with elevations. I was able to set points and see what approximimate pool would look like. When contractor laid it out on site it was very close to what I envisioned.
2 acres - FHM, GSH, PSC, RES, HBG, BG, LMB and YP
1 acre - filling with FMH, GSH, and PSC till fall 2020, then SMB and YP
I subscribe to PBM