Timelapse: Grindley Brook and beyond

I've got round to exporting some more timelapse to YouTube. This one is from just as we enter the staircase at Grindley Brook and goes to just past Bridge 54 at Cole Mere.



It's certainly better at one image every five seconds (of real time), but, of course, its hungrier in terms of memory. My timelapse camera has an 8GB SDHC card: at a time interval of 5" it records in chunks of about 300MB and seems to play back at about 2.5 frames per second, taking about 6 mins 50 secs to do so. Thus there are approximately 1025 images in each 300MB chunk, representing 1025 x 5 = 5125 seconds of real time, or just under an hour and a half. Hang on, that can't be right. One 6'50" chunk covers from Chirk Tunnel to Ellesmere Tunnel: 11 miles and two locks. Even with the current we didn't do that in an hour and a half! I've gone wrong in my calculations somewhere ...