Bluebulb Projects' The Measure of Things presents:
78 is about nine-tenths the number of Keys on a Piano.
In other words, it's 0.890 times the count of Keys on a Piano, and the count of Keys on a Piano is 1.10 times that amount.
(Moden layout; A0
Most modern keyboards have 88 keys, comprising seven octaves and an additional major third. A full-size, acoustic piano may have as many as 12,000 separate parts.