Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Interferometer and observing mode | Waveband | Limiting magnitude | Minimum baseline (m)\n(un-projected) | Maximum baseline (m) | Approx. no. visibility measurements per year\n(measurements per night x nights used per year) | Max ratio of no. phase / no. amplitude measurements\n(measure of imaging performance, 0 = none) | Accuracy of amplitude2 measurements | Accuracy of phase measurements\n(milli-radians) | Number of spectral channels\n(max in use simultaneously) | Comments |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| CHARA Array | V, R, I, J, H, K | 8 | 34 | 330 | 7500 | 0.7 | 1% | 10 | 30000 | Yes... 30000 in the visible band; maxiumum baseline 330-m |
| COAST visible | R, I | 7 | 4 | 60 | 2000 | 0.5 | 4% | 10 | 4? | 300 cloudy nights per year, maximum baseline 100-m |
| COAST infrared | J, H | 3 | 4 | 60 | 100 | 0.5 | 20% | 10 | 1 | 300 cloudy nights per year, maximum baseline 100-m |
| GI2T visible | R, I | 5 | 10 | 65 | 2000 | 0 | 10% | - | 400? | CLOSED in 2006 |
| IOTA | J, H, K | 7 | 6 | 30 | 10000 | 0.3 | 2% | 10 | 1? | Integrated optics beam combiner. CLOSED. |
| ISI | N | 0 | 10 | 50 | 5000 | 0.3 | 1% | 1 | 1000 | Maximum baseline 70-m |
| Keck Interferometer | H, K, L, N | 10.3 | 85 | 85 | 1000 | 0 | 4% | 1 | 330 | Nulling Key Science Underway - No imaging on a single baseline instrument; maximum baseline 11-m. CLOSED. |
| Keck Aperture Masking | J, H, K, L | 2 | 0.5 | 9 | 20000 | 0.9 | 20% | 10 | 1 | CLOSED. |
| MIRA 1.2 | R, I | 3 | 30 | 30 | 500 | 0 | 10% | - | 1 | Mid-Infrared |
| Navy Precision Optical Interferometer(NPOI) visible | V, R, I | 5 | 5 | 300 | 50000 | 0.7 | 4% | 10 | 16 | at NOFS; siderstats operational 4 x 1.8m added apertures in FY13. World's largest optical baseline-437m, 6-phased |
| Palomar Testbed Interferometer | J,H,K | 7 | 86 | 110 | 50000 | 0 | 2% | 0.1 | 5,10 | "dual-star" capable , No imaging on a single baseline instrument. CLOSED 2009. |
| SUSI | B, V, R, I | 5 | 5 | 640 | 5000 | 0 | 4% | 10 | 21 | No imaging on a single baseline instrument; Maximum baseline 160m |
| VLTI\n+UTs AMBER | J, H, K simultaneously | 7 | 46 | 130 | 400 | 0.3 | 1% | 10 | 2000 | Used for a few weeks per year. Longest overall VLTI Baseline 130m |
| VLTI\n+ATs AMBER | J, H, K simultaneously | 4 | 46 | 130 | 400 | 0.3 | 1% | 10 | 2000 | Longest overall VLTI Baseline 130m |
| VLTI\n+UTs VINCI | K | 11 | 46 | 130 | 400 | 0 | >1% | - | 1 | Integrated optics beam combiner. Longest overall VLTI Baseline 130m |
| VLTI\n+ATs VINCI | K | Never checked | 12 | 200 | 400 | 0 | >1% | - | 1 | Longest overall VLTI Baseline 130m |
| VLTI\n+UTs MIDI | N | 4.5 | 46 | 130 | 200 | 0 | 10% | - | 250 | Used for a few weeks per year. Longest overall VLTI Baseline 130m |
| VLTI\n+ATs MIDI | N | 4.5 | ? | 200 | 200 | 0 | 10% | - | 250 | VLTI inldes World's largest unfilled apertures (siderostats, 1.8-m, 8-m). Longest overall VLTI Baseline 130m |
Question:
what is the number of interferometers that use wavebands r?
Answer:
6