 Instead, it compromises on a 449-line frame (instead of the expected 450), with the back porch extended to 34 lines, and the front porch to 13, with an unaltered 2-line sync pulseand the active image taking up 89% of the total scan period rather than 91%.The monitor is triggered into synchronising at the higher frame scan rate (and, with digital displays such as LCDs, the higher horizontal pixel density) by use of a positive-polarity VSync pulse, versus the negative pulse of 60 Hz mode.Depending on manufacturer, the exact details of active period and front/back porch widths, particularly in the horizontal domain, may vary slightly.