You raise an important point; don't assume your line is long enough to comfortably reach the surface. If it's choppy or you're deploying from depth, it's not unusual for the line to be diagonal if there's a moderate current or wind topside. I find it's always sensible to have plenty of extra line available. From 30m, I would want at least a 45m line.I was recently separated from my group (4 of us) due to current and low visibility on a 20 meter wreck dive. Not knowing how far off I was I deployed my DSMB at 19M. I quickly learned I do not have 19M worth of string on my reel. I was about 3 meters short. I used the reel to pull me up to a safety atop then the rest of the way to the surface. Strongly recommend you measure the string length on your DSMB. Even if you don't plan on deploying at depth it's good to know what you have.