TPLENGTH is the length of the tapes in use at each site. For VLBA, Mark III, and Mark IV tapes, the length is in feet. Thick tapes, which are still in use within the EVN but are not allowed at the VLBA correlator, have roughly 8800 feet of usable length(see the section on tape lengths). Thin tapes used for most VLBA and Mark IV observations usually have 17600 feet of usable tape. The VLBA operations staff tries to make sure that all thin tapes have at least 17400 feet of usable tape by splicing in extra when needed. Note that the 200 ft difference amounts to 30 seconds at 80 ips (the speed for speed-up-factor 2 observations).
Note that changing the length of the tape is not sufficient to switch from thick to thin tape. In that case one usually also needs to modify the recording density
S2 tape length should be given in seconds, corresponding to Standard Play in a US VCR. A tape with label ST-120 (or SE-180) should be scheduled with TPLENGTH = 7200