I guess I was thinking of the classroom definitions rather than the field, where BM + BS might represent conversational content rather than Bench Mark + Back Sight. But, it is nice to see a sense of humor in these forums once in awhile.
Assuming you are using a level, the HI (height of instrument) is the elevation of the instrument relative to the benchmark. When you book it, you set up your instrument, write down the benchmark elevation in your book and shoot the benchmark (BM). Book the reading as your backsight (BS). Now add the BS shot to the BM elevation and that is your HI. Now you can shoot as many FS as you need with the one setup. To move your instrument, use your last FS. Calculate it elevation. Move the instrument. Shoot the last FS, but this time book the shot as a BS and repeat the HI calculation. With a total station, enter the required information and follow the instructions. KRS Services
