gauge question

Hello to all: I am making a gauge so that it works in FS2002. This is the mach indicator. It is of type of vertical sliding with the digits in the means. I programming in "C" The problem is that when I use the gauge the digit disappears for a moment and then reappears when the MACH change. For MACH 0.701 to .708 the numbers don't see. In 0.709 the numbers appear and they see up to 0.710, in 0.711 disappear until 0.718 and so forth. I made 2 gauges one of 2 digits (MACH 0.00) and one of 3 (MACH 0.000), in both it passes the same thing. In that of 2 digits each 0.08 and in that of 3 digits each 0.03. In FS2000 work fine. Is somebody able to help me?. Thank you very muchJose