The Heterodyne Integration TimE Calculator (HITEC) is a web-based tool for estimating required integration times for heterodyne observations. To start the calculation, users need to enter a number of parameters in various panels as described in details bellow:

	1. Using this panel you can select the receiver you wish to use. This will automatically update the box showing your desired frequency to the centre of the frequency band for that receiver. Alternatively you can simply type the frequency you wish to observe at directly into the frequency box and the correct receiver will be selected (or a warning message shown if you have selected a frequency that no receiver can tune to). Based on the frequency you entered the receiver temperature (Trx) will be calculated. The value for Trx is taken from a table in the file receiver.info. The Trx for HARP is the average of 16 receptors. Some of our receivers have 2 mixers in them (presently WxD) enabling the integration time to be halved although note that it is not possible to use both for all DAS modes, a warning will be shown if you try an illegal combination. Similarly some receivers feature sideband rejection enabling the selection of either Single Side Band (SSB) or Double Side Band (DSB) mode. Trx is higher for SSB but Tsys is colder due to the termination load being colder than the sky. Again a warning will be issued if you select this for a receiver that cannot reject one side band.
	2. Using this panel you can specify the weather conditions you wish to calculate your observing time in. These categories correspond to the weather bands that you specify on your PATT application form. HITEC contains a model of the atmospheric opacity at all frequencies for which the JCMT has receivers for each of these weatherbands (at Tau(225GHz)=0.5, 0.65, 0.1, 0.16, 0.25). Using this and the frequency you give for the observations it calculates your estimated Tsys value.
	3. Enter the source Declination (DEC) here. The expected average zenith angle (0 for zenith, 90 for horizon) will be calculated using the formula ZA_avg = 180/pi * acos( 0.9*cos( pi/180*(DEC-19.823) ) ) where pi=3.1416, the value 19.823 is the latitude of the JCMT, and the factor 0.9 is an approximation for the average zenith angle of the source during the 4 hours near the transit. You can also enter the zenith angle directly to include the extra thickness of the atmosphere at lower elevations. You also need to decide what setting on the ACSIS mode you wish to use. This can either be done from the pulldown menu or by entering directly the frequency resolution, either as a velocity or a frequency (this would be useful if you are planning to bin your data).
	4. Use this panel to set up the type of observations you wish to make. Position switching will spend approximately 50% of the time on an offsource reference position but will generally produce flat baselines. Frequency switch is much more efficient, spending close to 100% of the time on source but will produce wavy baselines that will not be suitable when wide lines are being observed. For producing maps, raster mapping is often the most efficient method with only one offsource reference taken per scan line. If you select this option you need to enter the size of your map (since the integration time will depend on the number of points per row that you select). Making small maps with HARP is most efficient by using the jiggle map. See the following document for detailed information about the various modes offered for heterodyne observations: 'Heterodyne MSBs'. For a detailed and technical discussion about the overhead, expected time and noise associated with different observing modes, see 'Heterodyne Obsmodes'
	5. You can select to enter either a desired 1 sigma rms Ta* noise level, in which case the on-source only integration time will be calculated, or an on-source only integration time can be entered in which case the 1 sigma rms Ta* noise level will be calculated.
	Output: after entering all the related parameters, click on the Calculate button, the expected final sensitivity or integration time (on-source only), and the total elapse time will be calculated and shown on a refreshed web page. The estimated system temperature, Tsys, calculated based on the given receiver temperature and the average atmospheric opacity, is also displayed. The format for the total elapse time depends on the amount of time calculated and can be hh:mm or mm:ss.