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To be precise, the MSL doesn't really indicate the gradient between stations. IR has strict guidelines for gradients in yards, stations and between stations (depending on kind of traffic expected). So, irrespective of the MSL of two successive stations, the track is always laid out in such a way that the gradients are within a limit. So, the MSL markings are practically of no use to the Loco Pilots. The LPs depend on the gradient markings provided all along the route, and their knowledge of the route (through their route learning) and the working timetable provided to them that indicates all the speed limits on the route.
For example, between Karjat and Lonavala, within a span of...
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27 km, the line ascends almost 500m. IN the VSKP-Kirandul section, between SUP-SMLG, the line ascends almost 1000m over a distance of 60km. However, the ruling gradient is very different between both sections.
The MSL markings are a relic from earlier days when they were the only way to determine the difference in elevation between different places. With the advent of satellite imagery, this has become redundant. But the practice is still continued as during the surveys for constructing new railway lines and stations, the elevations and MSL are also collected as a part of the Civil Engineering surveys.